Install headers in more clang relative locations

Fix Apple bug 9978441 by installing the headers in yet more locations so
that clang may find them when installed as a part of iOS SDKs.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/branches/apple@138209 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed