After a closer look, I think this patch is wrong: it changes the default search path without any compiler flags, while Clang shouldn't be looking at libc++ stuff without `-stdlib=libc++`, and even with that flag on, it should still only look at system default locations. Upstream suggests that to use custom built libc++, one should use `clang -stdlib=libc++ -nostdinc++ -I#{/path/to/headers} -L#{/path/to/libs}`. See "Get it and get involved!" section in http://libcxx.llvm.org/.