diff --git a/Modules/CMakeSystemSpecificInformation.cmake b/Modules/CMakeSystemSpecificInformation.cmake
index b5dc8d3ed7..70bcf5cb58 100644
--- a/Modules/CMakeSystemSpecificInformation.cmake
+++ b/Modules/CMakeSystemSpecificInformation.cmake
@@ -6,19 +6,6 @@
 # It is included after the compiler has been determined, so
 # we know things like the compiler name and if the compiler is gnu.
 
-# before cmake 2.6 these variables were set in cmMakefile.cxx. This is still
-# done to keep scripts and custom language and compiler modules working.
-# But they are reset here and set again in the platform files for the target
-# platform, so they can be used for testing the target platform instead
-# of testing the host platform.
-set(APPLE  )
-set(UNIX   )
-set(CYGWIN )
-set(MSYS )
-set(WIN32  )
-set(BSD )
-set(LINUX )
-
 function(_cmake_record_install_prefix )
   set(_CMAKE_SYSTEM_PREFIX_PATH_INSTALL_PREFIX_VALUE "${CMAKE_INSTALL_PREFIX}" PARENT_SCOPE)
   set(_CMAKE_SYSTEM_PREFIX_PATH_STAGING_PREFIX_VALUE "${CMAKE_STAGING_PREFIX}" PARENT_SCOPE)
diff --git a/Modules/CMakeSystemSpecificInitialize.cmake b/Modules/CMakeSystemSpecificInitialize.cmake
index 21bcd403ca..e87d868a8f 100644
--- a/Modules/CMakeSystemSpecificInitialize.cmake
+++ b/Modules/CMakeSystemSpecificInitialize.cmake
@@ -5,6 +5,19 @@
 # This file is included by cmGlobalGenerator::EnableLanguage.
 # It is included before the compiler has been determined.
 
+# before cmake 2.6 these variables were set in cmMakefile.cxx. This is still
+# done to keep scripts and custom language and compiler modules working.
+# But they are reset here and set again in the platform files for the target
+# platform, so they can be used for testing the target platform instead
+# of testing the host platform.
+unset(APPLE)
+unset(UNIX)
+unset(CYGWIN)
+unset(MSYS)
+unset(WIN32)
+unset(BSD)
+unset(LINUX)
+
 # The CMAKE_EFFECTIVE_SYSTEM_NAME is used to load compiler and compiler
 # wrapper configuration files. By default it equals to CMAKE_SYSTEM_NAME
 # but could be overridden in the ${CMAKE_SYSTEM_NAME}-Initialize files.
diff --git a/Modules/Platform/AIX-Initialize.cmake b/Modules/Platform/AIX-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/AIX-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/Android-Initialize.cmake b/Modules/Platform/Android-Initialize.cmake
index 63bc949170..2a2f6e21fd 100644
--- a/Modules/Platform/Android-Initialize.cmake
+++ b/Modules/Platform/Android-Initialize.cmake
@@ -23,6 +23,11 @@ if(CMAKE_SYSTEM_VERSION EQUAL 1)
   return()
 endif()
 
+include(Platform/Linux-Initialize)
+unset(LINUX)
+
+set(ANDROID 1)
+
 set(CMAKE_BUILD_TYPE_INIT "RelWithDebInfo")
 
 if(CMAKE_ANDROID_NDK_TOOLCHAIN_UNIFIED)
diff --git a/Modules/Platform/Android.cmake b/Modules/Platform/Android.cmake
index 05309883cd..f490f0e54a 100644
--- a/Modules/Platform/Android.cmake
+++ b/Modules/Platform/Android.cmake
@@ -4,11 +4,6 @@ if(CMAKE_ANDROID_NDK)
   include(${CMAKE_ANDROID_NDK}/build/cmake/hooks/pre/Android.cmake OPTIONAL)
 endif()
 
-include(Platform/Linux)
-unset(LINUX)
-
-set(ANDROID 1)
-
 # Natively compiling on an Android host doesn't need these flags to be reset.
 if(CMAKE_HOST_SYSTEM_NAME STREQUAL "Android")
   return()
diff --git a/Modules/Platform/BSDOS-Initialize.cmake b/Modules/Platform/BSDOS-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/BSDOS-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/BeOS-Initialize.cmake b/Modules/Platform/BeOS-Initialize.cmake
new file mode 100644
index 0000000000..ccdac6476e
--- /dev/null
+++ b/Modules/Platform/BeOS-Initialize.cmake
@@ -0,0 +1,2 @@
+set(BEOS 1)
+set(UNIX 1)
diff --git a/Modules/Platform/BeOS.cmake b/Modules/Platform/BeOS.cmake
index ef811bd9c3..e8573b95ba 100644
--- a/Modules/Platform/BeOS.cmake
+++ b/Modules/Platform/BeOS.cmake
@@ -1,5 +1,3 @@
-set(BEOS 1)
-
 set(CMAKE_DL_LIBS root be)
 set(CMAKE_C_COMPILE_OPTIONS_PIC "-fPIC")
 set(CMAKE_C_COMPILE_OPTIONS_PIE "-fPIE")
diff --git a/Modules/Platform/BlueGeneL-Initialize.cmake b/Modules/Platform/BlueGeneL-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/BlueGeneL-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/BlueGeneP-base.cmake b/Modules/Platform/BlueGeneP-base.cmake
index 7095dd87bc..3c06215680 100644
--- a/Modules/Platform/BlueGeneP-base.cmake
+++ b/Modules/Platform/BlueGeneP-base.cmake
@@ -49,11 +49,6 @@ set(CMAKE_SYSTEM_IGNORE_PATH
   /usr/X11R7/lib   /usr/X11R7/lib64   /usr/X11R7/include
 )
 
-#
-# Indicate that this is a unix-like system
-#
-set(UNIX 1)
-
 #
 # Library prefixes, suffixes, extra libs.
 #
diff --git a/Modules/Platform/BlueGeneP-dynamic-Initialize.cmake b/Modules/Platform/BlueGeneP-dynamic-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/BlueGeneP-dynamic-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/BlueGeneP-static-Initialize.cmake b/Modules/Platform/BlueGeneP-static-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/BlueGeneP-static-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/BlueGeneQ-base.cmake b/Modules/Platform/BlueGeneQ-base.cmake
index 94cb0a80e3..ea4b78919e 100644
--- a/Modules/Platform/BlueGeneQ-base.cmake
+++ b/Modules/Platform/BlueGeneQ-base.cmake
@@ -39,11 +39,6 @@ set(CMAKE_SYSTEM_IGNORE_PATH
   /usr/X11R7/lib   /usr/X11R7/lib64   /usr/X11R7/include
 )
 
-#
-# Indicate that this is a unix-like system
-#
-set(UNIX 1)
-
 #
 # Library prefixes, suffixes, extra libs.
 #
diff --git a/Modules/Platform/BlueGeneQ-dynamic-Initialize.cmake b/Modules/Platform/BlueGeneQ-dynamic-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/BlueGeneQ-dynamic-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/BlueGeneQ-static-Initialize.cmake b/Modules/Platform/BlueGeneQ-static-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/BlueGeneQ-static-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/CYGWIN-Initialize.cmake b/Modules/Platform/CYGWIN-Initialize.cmake
new file mode 100644
index 0000000000..c90c51e859
--- /dev/null
+++ b/Modules/Platform/CYGWIN-Initialize.cmake
@@ -0,0 +1,2 @@
+set(CYGWIN 1)
+set(UNIX 1)
diff --git a/Modules/Platform/CYGWIN.cmake b/Modules/Platform/CYGWIN.cmake
index 0b64496e60..cf5e732833 100644
--- a/Modules/Platform/CYGWIN.cmake
+++ b/Modules/Platform/CYGWIN.cmake
@@ -1,5 +1,3 @@
-set(CYGWIN 1)
-
 set(CMAKE_SHARED_LIBRARY_PREFIX "cyg")
 set(CMAKE_SHARED_LIBRARY_SUFFIX ".dll")
 set(CMAKE_SHARED_MODULE_PREFIX "cyg")
diff --git a/Modules/Platform/Catamount-Initialize.cmake b/Modules/Platform/Catamount-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/Catamount-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/CrayLinuxEnvironment-Initialize.cmake b/Modules/Platform/CrayLinuxEnvironment-Initialize.cmake
new file mode 100644
index 0000000000..32cd009347
--- /dev/null
+++ b/Modules/Platform/CrayLinuxEnvironment-Initialize.cmake
@@ -0,0 +1,4 @@
+# CrayLinuxEnvironment: loaded by users cross-compiling on a Cray front-end
+# node by specifying "-DCMAKE_SYSTEM_NAME=CrayLinuxEnvironment" to cmake
+
+set(UNIX 1)
diff --git a/Modules/Platform/CrayLinuxEnvironment.cmake b/Modules/Platform/CrayLinuxEnvironment.cmake
index b982b3f3cf..648806f57d 100644
--- a/Modules/Platform/CrayLinuxEnvironment.cmake
+++ b/Modules/Platform/CrayLinuxEnvironment.cmake
@@ -1,8 +1,6 @@
 # CrayLinuxEnvironment: loaded by users cross-compiling on a Cray front-end
 # node by specifying "-DCMAKE_SYSTEM_NAME=CrayLinuxEnvironment" to cmake
 
-set(UNIX 1)
-
 if(DEFINED ENV{CRAYOS_VERSION})
   set(CMAKE_SYSTEM_VERSION "$ENV{CRAYOS_VERSION}")
 elseif(DEFINED ENV{XTOS_VERSION})
diff --git a/Modules/Platform/DOS-Initialize.cmake b/Modules/Platform/DOS-Initialize.cmake
new file mode 100644
index 0000000000..10b0cbfedd
--- /dev/null
+++ b/Modules/Platform/DOS-Initialize.cmake
@@ -0,0 +1 @@
+set(DOS 1)
diff --git a/Modules/Platform/DOS.cmake b/Modules/Platform/DOS.cmake
index fc95936d34..856f4b15cb 100644
--- a/Modules/Platform/DOS.cmake
+++ b/Modules/Platform/DOS.cmake
@@ -1,5 +1,3 @@
-set(DOS 1)
-
 set(CMAKE_STATIC_LIBRARY_PREFIX "")
 set(CMAKE_STATIC_LIBRARY_SUFFIX ".lib")
 set(CMAKE_SHARED_LIBRARY_PREFIX "")
diff --git a/Modules/Platform/Darwin-Initialize.cmake b/Modules/Platform/Darwin-Initialize.cmake
index c2f18515b4..e253392acd 100644
--- a/Modules/Platform/Darwin-Initialize.cmake
+++ b/Modules/Platform/Darwin-Initialize.cmake
@@ -1,3 +1,6 @@
+set(APPLE 1)
+set(UNIX 1)
+
 # Ask xcode-select where to find /Developer or fall back to ancient location.
 execute_process(COMMAND xcode-select -print-path
   OUTPUT_VARIABLE _stdout
diff --git a/Modules/Platform/Darwin.cmake b/Modules/Platform/Darwin.cmake
index a6c86f1303..48a9065c8d 100644
--- a/Modules/Platform/Darwin.cmake
+++ b/Modules/Platform/Darwin.cmake
@@ -1,5 +1,3 @@
-set(APPLE 1)
-
 if(CMAKE_SYSTEM_NAME STREQUAL "iOS" OR CMAKE_SYSTEM_NAME STREQUAL "tvOS" OR CMAKE_SYSTEM_NAME STREQUAL "watchOS")
   if(NOT DEFINED CMAKE_MACOSX_BUNDLE)
     set(CMAKE_MACOSX_BUNDLE ON)
diff --git a/Modules/Platform/DragonFly-Initialize.cmake b/Modules/Platform/DragonFly-Initialize.cmake
new file mode 100644
index 0000000000..ded94a923f
--- /dev/null
+++ b/Modules/Platform/DragonFly-Initialize.cmake
@@ -0,0 +1,2 @@
+include(Platform/FreeBSD-Initialize)
+set(BSD "DragonFlyBSD")
diff --git a/Modules/Platform/DragonFly.cmake b/Modules/Platform/DragonFly.cmake
index 994ba7931f..12e5f3cccf 100644
--- a/Modules/Platform/DragonFly.cmake
+++ b/Modules/Platform/DragonFly.cmake
@@ -3,7 +3,6 @@
 # see http://archive.netbsd.se/?ml=dfbsd-users&a=2007-07&m=4678361
 
 include(Platform/FreeBSD)
-set(BSD "DragonFlyBSD")
 
 # DragonFly BSD requires -z origin to enable $ORIGIN expansion in RPATH.
 # This is not required for FreeBSD since 10.2-RELEASE.
diff --git a/Modules/Platform/FreeBSD-Initialize.cmake b/Modules/Platform/FreeBSD-Initialize.cmake
new file mode 100644
index 0000000000..8c62a04459
--- /dev/null
+++ b/Modules/Platform/FreeBSD-Initialize.cmake
@@ -0,0 +1,2 @@
+set(BSD "FreeBSD")
+set(UNIX 1)
diff --git a/Modules/Platform/FreeBSD.cmake b/Modules/Platform/FreeBSD.cmake
index 9cd93998fe..bd5a78638e 100644
--- a/Modules/Platform/FreeBSD.cmake
+++ b/Modules/Platform/FreeBSD.cmake
@@ -1,4 +1,3 @@
-set(BSD "FreeBSD")
 set(CMAKE_DL_LIBS "")
 set(CMAKE_C_COMPILE_OPTIONS_PIC "-fPIC")
 set(CMAKE_C_COMPILE_OPTIONS_PIE "-fPIE")
diff --git a/Modules/Platform/Fuchsia-Initialize.cmake b/Modules/Platform/Fuchsia-Initialize.cmake
new file mode 100644
index 0000000000..74b880a5f1
--- /dev/null
+++ b/Modules/Platform/Fuchsia-Initialize.cmake
@@ -0,0 +1 @@
+set(FUCHSIA 1)
diff --git a/Modules/Platform/Fuchsia.cmake b/Modules/Platform/Fuchsia.cmake
index 4b13805065..ad3a36592f 100644
--- a/Modules/Platform/Fuchsia.cmake
+++ b/Modules/Platform/Fuchsia.cmake
@@ -1,5 +1,3 @@
-set(FUCHSIA 1)
-
 set(CMAKE_DL_LIBS "")
 set(CMAKE_C_COMPILE_OPTIONS_PIC "-fPIC")
 set(CMAKE_C_COMPILE_OPTIONS_PIE "-fPIE")
diff --git a/Modules/Platform/GNU-Initialize.cmake b/Modules/Platform/GNU-Initialize.cmake
index 37875ab429..3db6cff184 100644
--- a/Modules/Platform/GNU-Initialize.cmake
+++ b/Modules/Platform/GNU-Initialize.cmake
@@ -1 +1,3 @@
+set(UNIX 1)
+
 set(CMAKE_LIBRARY_ARCHITECTURE_REGEX "[a-z0-9_]+(-[a-z0-9_]+)?-gnu[a-z0-9_]*")
diff --git a/Modules/Platform/HP-UX-Initialize.cmake b/Modules/Platform/HP-UX-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/HP-UX-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/Haiku-Initialize.cmake b/Modules/Platform/Haiku-Initialize.cmake
new file mode 100644
index 0000000000..fa9d45644e
--- /dev/null
+++ b/Modules/Platform/Haiku-Initialize.cmake
@@ -0,0 +1,2 @@
+set(HAIKU 1)
+set(UNIX 1)
diff --git a/Modules/Platform/Haiku.cmake b/Modules/Platform/Haiku.cmake
index b8e3ba6280..7d9a73771d 100644
--- a/Modules/Platform/Haiku.cmake
+++ b/Modules/Platform/Haiku.cmake
@@ -1,6 +1,3 @@
-set(HAIKU 1)
-set(UNIX 1)
-
 set(CMAKE_DL_LIBS "")
 set(CMAKE_SHARED_LIBRARY_C_FLAGS "-fPIC")
 set(CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS "-shared")
diff --git a/Modules/Platform/Linux-Initialize.cmake b/Modules/Platform/Linux-Initialize.cmake
index 6d9cbae486..7166b20e8b 100644
--- a/Modules/Platform/Linux-Initialize.cmake
+++ b/Modules/Platform/Linux-Initialize.cmake
@@ -1,2 +1,5 @@
+set(LINUX 1)
+set(UNIX 1)
+
 # Match multiarch library directory names.
 set(CMAKE_LIBRARY_ARCHITECTURE_REGEX "[a-z0-9_]+(-[a-z0-9_]+)?-linux-gnu[a-z0-9_]*")
diff --git a/Modules/Platform/Linux.cmake b/Modules/Platform/Linux.cmake
index 1f2d8e6ce1..97a116f223 100644
--- a/Modules/Platform/Linux.cmake
+++ b/Modules/Platform/Linux.cmake
@@ -1,4 +1,3 @@
-set(LINUX 1)
 set(CMAKE_DL_LIBS "dl")
 set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG "-Wl,-rpath,")
 set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG_SEP ":")
diff --git a/Modules/Platform/MP-RAS-Initialize.cmake b/Modules/Platform/MP-RAS-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/MP-RAS-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/MSYS-Initialize.cmake b/Modules/Platform/MSYS-Initialize.cmake
new file mode 100644
index 0000000000..cc33f877bb
--- /dev/null
+++ b/Modules/Platform/MSYS-Initialize.cmake
@@ -0,0 +1,2 @@
+set(MSYS 1)
+include(Platform/CYGWIN-Initialize)
diff --git a/Modules/Platform/MSYS.cmake b/Modules/Platform/MSYS.cmake
index 96fa36f580..468718d005 100644
--- a/Modules/Platform/MSYS.cmake
+++ b/Modules/Platform/MSYS.cmake
@@ -1,4 +1,3 @@
-set(MSYS 1)
 include(Platform/CYGWIN)
 set(CMAKE_SHARED_LIBRARY_PREFIX "msys-")
 set(CMAKE_SHARED_MODULE_PREFIX "msys-")
diff --git a/Modules/Platform/Midipix-Initialize.cmake b/Modules/Platform/Midipix-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/Midipix-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/NetBSD-Initialize.cmake b/Modules/Platform/NetBSD-Initialize.cmake
new file mode 100644
index 0000000000..055216d804
--- /dev/null
+++ b/Modules/Platform/NetBSD-Initialize.cmake
@@ -0,0 +1,2 @@
+set(BSD "NetBSD")
+set(UNIX 1)
diff --git a/Modules/Platform/NetBSD.cmake b/Modules/Platform/NetBSD.cmake
index 52c65942f2..ab859239fb 100644
--- a/Modules/Platform/NetBSD.cmake
+++ b/Modules/Platform/NetBSD.cmake
@@ -1,4 +1,3 @@
-set(BSD "NetBSD")
 set(CMAKE_DL_LIBS "")
 set(CMAKE_C_COMPILE_OPTIONS_PIC "-fPIC")
 set(CMAKE_C_COMPILE_OPTIONS_PIE "-fPIE")
diff --git a/Modules/Platform/OSF1-Initialize.cmake b/Modules/Platform/OSF1-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/OSF1-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/OpenBSD-Initialize.cmake b/Modules/Platform/OpenBSD-Initialize.cmake
new file mode 100644
index 0000000000..dee9a877ec
--- /dev/null
+++ b/Modules/Platform/OpenBSD-Initialize.cmake
@@ -0,0 +1,2 @@
+include(Platform/NetBSD-Initialize)
+set(BSD "OpenBSD")
diff --git a/Modules/Platform/OpenBSD.cmake b/Modules/Platform/OpenBSD.cmake
index 51ea60dff2..97e2a6a83e 100644
--- a/Modules/Platform/OpenBSD.cmake
+++ b/Modules/Platform/OpenBSD.cmake
@@ -1,5 +1,4 @@
 include(Platform/NetBSD)
-set(BSD "OpenBSD")
 
 # On OpenBSD, the compile time linker does not share it's configuration with
 # the runtime linker.  This will extract the library search paths from the
diff --git a/Modules/Platform/OpenVMS-Initialize.cmake b/Modules/Platform/OpenVMS-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/OpenVMS-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/QNX-Initialize.cmake b/Modules/Platform/QNX-Initialize.cmake
index 21a2cdde7b..c74ff049fd 100644
--- a/Modules/Platform/QNX-Initialize.cmake
+++ b/Modules/Platform/QNX-Initialize.cmake
@@ -1,2 +1,3 @@
+set(QNXNTO 1)
 include(Platform/GNU-Initialize)
 unset(CMAKE_LIBRARY_ARCHITECTURE_REGEX)
diff --git a/Modules/Platform/QNX.cmake b/Modules/Platform/QNX.cmake
index f0933141e9..be105a0ea5 100644
--- a/Modules/Platform/QNX.cmake
+++ b/Modules/Platform/QNX.cmake
@@ -1,5 +1,3 @@
-set(QNXNTO 1)
-
 include(Platform/GNU)
 
 set(CMAKE_DL_LIBS "")
diff --git a/Modules/Platform/RISCos-Initialize.cmake b/Modules/Platform/RISCos-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/RISCos-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/SCO_SV-Initialize.cmake b/Modules/Platform/SCO_SV-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/SCO_SV-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/SINIX-Initialize.cmake b/Modules/Platform/SINIX-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/SINIX-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/SerenityOS-Initialize.cmake b/Modules/Platform/SerenityOS-Initialize.cmake
new file mode 100644
index 0000000000..e6ad610a4b
--- /dev/null
+++ b/Modules/Platform/SerenityOS-Initialize.cmake
@@ -0,0 +1,2 @@
+set(SERENITYOS 1)
+set(UNIX 1)
diff --git a/Modules/Platform/SerenityOS.cmake b/Modules/Platform/SerenityOS.cmake
index dc4f369dc0..fa3d3ce285 100644
--- a/Modules/Platform/SerenityOS.cmake
+++ b/Modules/Platform/SerenityOS.cmake
@@ -1,6 +1,3 @@
-
-set(SERENITYOS 1)
-
 set(CMAKE_DL_LIBS "")
 set(CMAKE_SHARED_LIBRARY_RPATH_ORIGIN_TOKEN "\$ORIGIN")
 set(CMAKE_SHARED_LIBRARY_SUFFIX ".so")
diff --git a/Modules/Platform/SunOS-Initialize.cmake b/Modules/Platform/SunOS-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/SunOS-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/Tru64-Initialize.cmake b/Modules/Platform/Tru64-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/Tru64-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/ULTRIX-Initialize.cmake b/Modules/Platform/ULTRIX-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/ULTRIX-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/UNIX_SV-Initialize.cmake b/Modules/Platform/UNIX_SV-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/UNIX_SV-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/UnixPaths.cmake b/Modules/Platform/UnixPaths.cmake
index 8a0ad23905..32bc7bdf90 100644
--- a/Modules/Platform/UnixPaths.cmake
+++ b/Modules/Platform/UnixPaths.cmake
@@ -12,6 +12,9 @@ if(__UNIX_PATHS_INCLUDED)
 endif()
 set(__UNIX_PATHS_INCLUDED 1)
 
+# Since CMake 3.27, the Platform/<os>-Initialize modules set UNIX
+# if the corresponding Platform/<os> modules includes UnixPaths.
+# Retain the setting here to support externally-maintained platform modules.
 set(UNIX 1)
 
 # also add the install directory of the running cmake to the search directories
diff --git a/Modules/Platform/UnixWare-Initialize.cmake b/Modules/Platform/UnixWare-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/UnixWare-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/Windows-Initialize.cmake b/Modules/Platform/Windows-Initialize.cmake
new file mode 100644
index 0000000000..ecb2cf047d
--- /dev/null
+++ b/Modules/Platform/Windows-Initialize.cmake
@@ -0,0 +1 @@
+set(WIN32 1)
diff --git a/Modules/Platform/Windows.cmake b/Modules/Platform/Windows.cmake
index d8b3957818..8697e7a7fa 100644
--- a/Modules/Platform/Windows.cmake
+++ b/Modules/Platform/Windows.cmake
@@ -1,13 +1,3 @@
-set(WIN32 1)
-
-if(CMAKE_SYSTEM_NAME STREQUAL "WindowsCE")
-  set(WINCE 1)
-elseif(CMAKE_SYSTEM_NAME STREQUAL "WindowsPhone")
-  set(WINDOWS_PHONE 1)
-elseif(CMAKE_SYSTEM_NAME STREQUAL "WindowsStore")
-  set(WINDOWS_STORE 1)
-endif()
-
 set(CMAKE_STATIC_LIBRARY_PREFIX "")
 set(CMAKE_STATIC_LIBRARY_SUFFIX ".lib")
 set(CMAKE_SHARED_LIBRARY_PREFIX "")          # lib
diff --git a/Modules/Platform/WindowsCE-Initialize.cmake b/Modules/Platform/WindowsCE-Initialize.cmake
new file mode 100644
index 0000000000..32351a9092
--- /dev/null
+++ b/Modules/Platform/WindowsCE-Initialize.cmake
@@ -0,0 +1,2 @@
+include(Platform/Windows-Initialize)
+set(WINCE 1)
diff --git a/Modules/Platform/WindowsPhone-Initialize.cmake b/Modules/Platform/WindowsPhone-Initialize.cmake
new file mode 100644
index 0000000000..c591881100
--- /dev/null
+++ b/Modules/Platform/WindowsPhone-Initialize.cmake
@@ -0,0 +1,2 @@
+include(Platform/Windows-Initialize)
+set(WINDOWS_PHONE 1)
diff --git a/Modules/Platform/WindowsStore-Initialize.cmake b/Modules/Platform/WindowsStore-Initialize.cmake
new file mode 100644
index 0000000000..43374c2c08
--- /dev/null
+++ b/Modules/Platform/WindowsStore-Initialize.cmake
@@ -0,0 +1,2 @@
+include(Platform/Windows-Initialize)
+set(WINDOWS_STORE 1)
diff --git a/Modules/Platform/Xenix-Initialize.cmake b/Modules/Platform/Xenix-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/Xenix-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/eCos-Initialize.cmake b/Modules/Platform/eCos-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/eCos-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)
diff --git a/Modules/Platform/syllable-Initialize.cmake b/Modules/Platform/syllable-Initialize.cmake
new file mode 100644
index 0000000000..0b117a7b2f
--- /dev/null
+++ b/Modules/Platform/syllable-Initialize.cmake
@@ -0,0 +1 @@
+set(UNIX 1)