build: avoid generator expression usage for compiler swap

When using the monorepo, it seems that even if Swift is built
standalone, we would see the target as imported and attempt to use the
generator expression, which would not resolve.

Author: compnerd

cmake/modules/SwiftWindowsSupport.cmake

@@ -84,9 +84,9 @@ endfunction()
 macro(swift_swap_compiler_if_needed target)
   if(NOT CMAKE_C_COMPILER_ID MATCHES Clang)
     if(CMAKE_SYSTEM_NAME STREQUAL CMAKE_HOST_SYSTEM_NAME)
-      get_target_property(IMPORTED clang IMPORTED)
-      if(IMPORTED)
-        set(CLANG_LOCATION $<TARGET_FILE_DIR:clang>)
+      if(SWIFT_BUILT_STANDALONE)
+        get_target_property(CLANG_LOCATION clang LOCATION)
+        get_filename_component(CLANG_LOCATION ${CLANG_LOCATION} DIRECTORY)
       else()
         set(CLANG_LOCATION ${LLVM_RUNTIME_OUTPUT_INTDIR})
       endif()