[CMake] Fix the setting of LIBCXX_HEADER_DIR in standalone build
This is an alternative approach to r337727 which broke the build
because libc++ headers were copied into the location outside of
directories used by Clang. This change sets LIBCXX_HEADER_DIR to
different values depending on whether libc++ is being built as
part of LLVM w/ per-target multiarch runtime, LLVM or standalone.
Differential Revision: https://reviews.llvm.org/D49711
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@337833 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed