Build: Use imported target ZLIB::ZLIB instead of variables

Source/Modules/CMakeBuildUtilities.cmake

@@ -114,18 +114,20 @@ endif()
 
 #---------------------------------------------------------------------
 # Build zlib library for Curl, CMake, and CTest.
-set(CMAKE_ZLIB_HEADER "cm_zlib.h")
 if(CMAKE_USE_SYSTEM_ZLIB)
   find_package(ZLIB)
   if(NOT ZLIB_FOUND)
     message(FATAL_ERROR
       "CMAKE_USE_SYSTEM_ZLIB is ON but a zlib is not found!")
   endif()
-  set(CMAKE_ZLIB_INCLUDES ${ZLIB_INCLUDE_DIR})
-  set(CMAKE_ZLIB_LIBRARIES ${ZLIB_LIBRARIES})
 else()
-  set(CMAKE_ZLIB_INCLUDES ${CMake_SOURCE_DIR}/Utilities)
-  set(CMAKE_ZLIB_LIBRARIES cmzlib)
+  if(NOT POLICY CMP0102) # CMake < 3.17
+    # Store in cache to protect from mark_as_advanced.
+    set(ZLIB_INCLUDE_DIR ${CMake_SOURCE_DIR}/Utilities CACHE PATH "")
+  else()
+    set(ZLIB_INCLUDE_DIR ${CMake_SOURCE_DIR}/Utilities)
+  endif()
+  set(ZLIB_LIBRARY cmzlib)
   set(WITHOUT_ZLIB_DLL "")
   set(WITHOUT_ZLIB_DLL_WITH_LIB cmzlib)
   set(ZLIB_DLL "")
@@ -134,6 +136,7 @@ else()
   set(ZLIB_WINAPI_COMPILED 0)
   set(ZLIB_WINAPI_WITH_LIB cmzlib)
   add_subdirectory(Utilities/cmzlib)
+  add_library(ZLIB::ZLIB ALIAS cmzlib)
   CMAKE_SET_TARGET_FOLDER(cmzlib "Utilities/3rdParty")
 endif()
 
@@ -148,9 +151,6 @@ if(CMAKE_USE_SYSTEM_CURL)
   set(CMAKE_CURL_INCLUDES ${CURL_INCLUDE_DIRS})
   set(CMAKE_CURL_LIBRARIES ${CURL_LIBRARIES})
 else()
-  set(CURL_SPECIAL_ZLIB_H ${CMAKE_ZLIB_HEADER})
-  set(CURL_SPECIAL_LIBZ_INCLUDES ${CMAKE_ZLIB_INCLUDES})
-  set(CURL_SPECIAL_LIBZ ${CMAKE_ZLIB_LIBRARIES})
   set(CMAKE_CURL_INCLUDES)
   set(CMAKE_CURL_LIBRARIES cmcurl)
   if(CMAKE_TESTS_CDASH_SERVER)
@@ -263,8 +263,6 @@ if(CMAKE_USE_SYSTEM_LIBARCHIVE)
 else()
   set(EXPAT_INCLUDE_DIR ${CMAKE_EXPAT_INCLUDES})
   set(EXPAT_LIBRARY ${CMAKE_EXPAT_LIBRARIES})
-  set(ZLIB_INCLUDE_DIR ${CMAKE_ZLIB_INCLUDES})
-  set(ZLIB_LIBRARY ${CMAKE_ZLIB_LIBRARIES})
   add_compile_definitions(LIBARCHIVE_STATIC)
   set(ENABLE_MBEDTLS OFF)
   set(ENABLE_NETTLE OFF)