[CMake] Put headers relative to clang
[CMake] Put headers relative to clang

When libcxx isn't building with an installed LLVM we copy the libcxx headers into the LLVM build directory so that a clang in that build tree can find the headers relative to itself.

This is only important in situations where you don't have headers installed under /, which is common these days on Darwin.

git-svn-id: 756ef344af921d95d562d9e9f9389127a89a6314@289963 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx,llvm-mirror/libcxx