In r280108 I tried to make the headers copy relative to LLVM_BINARY_DIR, and the intent was that it would only happen on in-tree builds or runtimes directory builds. It didn't actually work that way.
This patch adds a check for CMAKE_SOURCE_DIR being equal to CMAKE_CURRENT_SOURCE_DIR. In this case we set a variable LIBCXX_USING_INSTLLED_LLVM. This doesn't necessarily mean the LLVM is installed (it could be a build directory), but it means we need to treat the LLVM directory as read-only.
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@280400 91177308-0d34-0410-b5e6-96231b3b80d8
2e3538460a