build: remove ALL_POSIX_PLATFORMS which is no longer used

Cleanup some CMake logic that we no longer need as the entire code base
now builds on all the targets.

Author: compnerd

cmake/modules/AddSwift.cmake

@@ -1693,7 +1693,6 @@ function(add_swift_target_library name)
   if("${SWIFTLIB_TARGET_SDKS}" STREQUAL "")
     set(SWIFTLIB_TARGET_SDKS ${SWIFT_SDKS})
   endif()
-  list_replace(SWIFTLIB_TARGET_SDKS ALL_POSIX_PLATFORMS "ALL_APPLE_PLATFORMS;ANDROID;CYGWIN;FREEBSD;LINUX;HAIKU")
   list_replace(SWIFTLIB_TARGET_SDKS ALL_APPLE_PLATFORMS "${SWIFT_APPLE_PLATFORMS}")
 
   # All Swift code depends on the standard library, except for the standard