Merge pull request swiftlang#25460 from compnerd/you-must-mine-more-vespene-gas

build: query the resource dir when needed

Author: compnerd

stdlib/public/SwiftShims/CMakeLists.txt

@@ -84,7 +84,15 @@ endif()
 # First extract the "version" used for Clang's resource directory.
 string(REGEX MATCH "[0-9]+\\.[0-9]+(\\.[0-9]+)?" CLANG_VERSION
   "${LLVM_PACKAGE_VERSION}")
-set(clang_headers_location "${LLVM_LIBRARY_OUTPUT_INTDIR}/clang/${CLANG_VERSION}")
+if(NOT SWIFT_INCLUDE_TOOLS AND SWIFT_BUILD_RUNTIME_WITH_HOST_COMPILER)
+  execute_process(COMMAND ${CMAKE_C_COMPILER} -print-resource-dir
+    OUTPUT_VARIABLE clang_headers_location
+    OUTPUT_STRIP_TRAILING_WHITESPACE
+    ERROR_QUIET)
+  message(STATUS "using clang resource directory: ${clang_headers_location}")
+else()
+  set(clang_headers_location "${LLVM_LIBRARY_OUTPUT_INTDIR}/clang/${CLANG_VERSION}")
+endif()
 
 if("${CMAKE_SYSTEM_NAME}" STREQUAL "Windows")
   set(cmake_symlink_option "copy_directory")