Merge pull request swiftlang#20107 from compnerd/frontend-is-not-cc

Author: swift-ci

cmake/modules/AddSwift.cmake

@@ -818,16 +818,16 @@ function(_add_swift_library_single target name)
   endif()
 
   if("${SWIFTLIB_SINGLE_SDK}" STREQUAL "WINDOWS")
-    swift_windows_include_for_arch(${SWIFTLIB_SINGLE_ARCHITECTURE} SWIFTLIB_INCLUDE)
     if(NOT "${CMAKE_C_COMPILER_ID}" STREQUAL "MSVC")
       swift_windows_generate_sdk_vfs_overlay(SWIFTLIB_SINGLE_VFS_OVERLAY_FLAGS)
       foreach(flag ${SWIFTLIB_SINGLE_VFS_OVERLAY_FLAGS})
         list(APPEND SWIFTLIB_SINGLE_SWIFT_COMPILE_FLAGS -Xcc;${flag})
         list(APPEND SWIFTLIB_SINGLE_C_COMPILE_FLAGS ${flag})
       endforeach()
     endif()
+    swift_windows_include_for_arch(${SWIFTLIB_SINGLE_ARCHITECTURE} SWIFTLIB_INCLUDE)
     foreach(directory ${SWIFTLIB_INCLUDE})
-      list(APPEND SWIFTLIB_SINGLE_SWIFT_COMPILE_FLAGS -Xfrontend;-I${directory})
+      list(APPEND SWIFTLIB_SINGLE_SWIFT_COMPILE_FLAGS -Xcc;-isystem;-Xcc;${directory})
     endforeach()
     if("${SWIFTLIB_SINGLE_ARCHITECTURE}" MATCHES arm)
       list(APPEND SWIFTLIB_SINGLE_SWIFT_COMPILE_FLAGS -Xcc;-D_ARM_WINAPI_PARTITION_DESKTOP_SDK_AVAILABLE)