Add SWIFT_PLATFORMS_USING_ISYSROOT to list platforms that should be building with -isysroot

Author: kubamracek

CMakeLists.txt

@@ -543,6 +543,9 @@ set(SWIFT_DARWIN_EMBEDDED_VARIANTS "^(iphoneos|iphonesimulator|appletvos|appletv
 #  endif()
 set(SWIFT_APPLE_PLATFORMS "IOS" "IOS_SIMULATOR" "TVOS" "TVOS_SIMULATOR" "WATCHOS" "WATCHOS_SIMULATOR" "OSX")
 
+# A convenient list of platforms that should use -isysroot ... when building.
+set(SWIFT_PLATFORMS_USING_ISYSROOT SWIFT_APPLE_PLATFORMS "FREESTANDING")
+
 # Configuration flags passed to all of our invocations of gyb.  Try to
 # avoid making up new variable names here if you can find a CMake
 # variable that will do the job.

cmake/modules/AddSwift.cmake

@@ -93,7 +93,7 @@ function(_add_host_variant_c_compile_link_flags name)
 
   set(_sysroot
     "${SWIFT_SDK_${SWIFT_HOST_VARIANT_SDK}_ARCH_${SWIFT_HOST_VARIANT_ARCH}_PATH}")
-  if(SWIFT_HOST_VARIANT_SDK IN_LIST SWIFT_APPLE_PLATFORMS)
+  if(SWIFT_HOST_VARIANT_SDK IN_LIST SWIFT_PLATFORMS_USING_ISYSROOT)
     target_compile_options(${name} PRIVATE -isysroot;${_sysroot})
   elseif(NOT SWIFT_COMPILER_IS_MSVC_LIKE AND NOT "${_sysroot}" STREQUAL "/")
     target_compile_options(${name} PRIVATE --sysroot=${_sysroot})

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -98,7 +98,7 @@ function(_add_target_variant_c_compile_link_flags)
   endif()
 
   set(_sysroot "${SWIFT_SDK_${CFLAGS_SDK}_ARCH_${CFLAGS_ARCH}_PATH}")
-  if(IS_DARWIN)
+  if(CFLAGS_SDK IN_LIST SWIFT_PLATFORMS_USING_ISYSROOT)
     list(APPEND result "-isysroot" "${_sysroot}")
   elseif(NOT SWIFT_COMPILER_IS_MSVC_LIKE AND NOT "${_sysroot}" STREQUAL "/")
     list(APPEND result "--sysroot=${_sysroot}")