Apple的Xcode附带了LLVM，但它不是开源版本.例如，Mac不会安装一些clang额外的工具.因此，至少苹果公司已经修改了CMakeLists.txt.您可以在 Apple开源.

Apple's Xcode ship with LLVM, but it is not the open source version. For example, some clang extra tool won't be installed to you Mac. So at least, Apple has modify CMakeLists.txt. You can read the CMakeLists.txt or Makefile in apple open source.

这只是一个建议，也许没有帮助.

This is only a suggestion, maybe is not helpful.

另一个: index.file 显示了将Xcode LLVM 9映射到Clang/LLVM 4.0

Another: index.file shows Xcode LLVM 9 map to Clang/LLVM 4.0.