RPATH: Record support for $ORIGIN on various *BSD

All of NetBSD, FreeBSD, OpenBSD and DragonFly BSD support `$ORIGIN`,
but the last two require `-z origin` as documented at

    https://lekensteyn.nl/rpath.html

The `-z origin` option causes a flag bit to be set and has no effect if
the `RPATH` does not contain expandable tokens.

Modules/Platform/DragonFly.cmake

@@ -3,3 +3,7 @@
 # see http://archive.netbsd.se/?ml=dfbsd-users&a=2007-07&m=4678361
 
 include(Platform/FreeBSD)
+
+# DragonFly BSD requires -z origin to enable $ORIGIN expansion in RPATH.
+# This is not required for FreeBSD since 10.2-RELEASE.
+set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG "-Wl,-z,origin,-rpath,")

Modules/Platform/FreeBSD.cmake

@@ -6,6 +6,8 @@ set(CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS "-shared")       # -shared
 set(CMAKE_SHARED_LIBRARY_LINK_C_FLAGS "")         # +s, flag for exe link to use shared lib
 set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG "-Wl,-rpath,")       # -rpath
 set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG_SEP ":")   # : or empty
+# Does not require -z origin since 10.2-RELEASE
+set(CMAKE_SHARED_LIBRARY_RPATH_ORIGIN_TOKEN "\$ORIGIN")
 set(CMAKE_SHARED_LIBRARY_RPATH_LINK_C_FLAG "-Wl,-rpath-link,")
 set(CMAKE_SHARED_LIBRARY_SONAME_C_FLAG "-Wl,-soname,")
 set(CMAKE_EXE_EXPORTS_C_FLAG "-Wl,--export-dynamic")

Modules/Platform/NetBSD.cmake

@@ -6,6 +6,7 @@ set(CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS "-shared")       # -shared
 set(CMAKE_SHARED_LIBRARY_LINK_C_FLAGS "")         # +s, flag for exe link to use shared lib
 set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG "-Wl,-rpath,")       # -rpath
 set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG_SEP ":")   # : or empty
+set(CMAKE_SHARED_LIBRARY_RPATH_ORIGIN_TOKEN "\$ORIGIN")
 set(CMAKE_SHARED_LIBRARY_RPATH_LINK_C_FLAG "-Wl,-rpath-link,")
 set(CMAKE_SHARED_LIBRARY_SONAME_C_FLAG "-Wl,-soname,")
 set(CMAKE_EXE_EXPORTS_C_FLAG "-Wl,--export-dynamic")

Modules/Platform/OpenBSD.cmake

@@ -15,6 +15,10 @@ if(NOT CMAKE_PLATFORM_RUNTIME_PATH)
          "${LDCONFIG_HINTS}")
 endif()
 
+# OpenBSD requires -z origin to enable $ORIGIN expansion in RPATH.
+# This is not required for NetBSD.
+set(CMAKE_SHARED_LIBRARY_RUNTIME_C_FLAG "-Wl,-z,origin,-rpath,")
+
 set_property(GLOBAL PROPERTY FIND_LIBRARY_USE_OPENBSD_VERSIONING 1)
 
 # OpenBSD has no multilib