How exaclly do I hack clang to search for system headers?

I having a hard understanding this.
“Look for the comment “FIXME: temporary hack: hard-coded paths” in clang/lib/Frontend/InitHeaderSearch.cpp and change the lines below to include that path.” What changes exactly? It’s so vague that it needs an example. Should the header search like the one in g++ be implement right about now? So that I don’t have to manually hack it every time?

Thanks for your time.