The clang builtins for source file location (e.g. like __builtin_FILE()) don't seem to be present even with Xcode 11 beta.
They've been in clang++ upstream release for some time now. When will they be made available in Xcode Clang?
They can be used to implement a functional std::source_location even without C++20 library support, which while not a "show stopper", is certainly far superior to the tradition preprocessor based method of obtaining this information (hence its adoption in the standard).