Update paths in libc++ build instructions. Patch from Jonathan Anderson.

llvm-svn: 255561
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 08ce75b6c653c8af6b4c43b91ee6aa61b61d1222
1 file changed