[CMake] Set library dir to be LLVM's intermediate output dir

This matches the behavior of libc++abi and libc++ and ensures that
we get a working toolchain when building libunwind as part of LLVM.

Differential Revision: https://reviews.llvm.org/D34375

git-svn-id: https://llvm.org/svn/llvm-project/libunwind/trunk@308380 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed