[CMake] Use libcxx targets for in-tree sanitizer C++ ABI

When in-tree libcxx is selected as the sanitizer C++ ABI, use libcxx
targets rather than libcxxabi and libunwind, since those may not be
available on all platforms (Windows for example).

Differential Revision: https://reviews.llvm.org/D134855

GitOrigin-RevId: 7dbdffefb768062f28599c256b5e013ee26ff04e