build: Start sketching code to allow grafting libc++ build into LLVM/Clang build if
libc++ is checked out into llvm/projects.
 - WIP, not on by default yet.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@113924 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed