[libcxxabi] Allow building with sanitizers enabled

Summary:
I copied the sanitizer-related logic in libcxx/lib/CMakeLists.txt. In
the future, it would be great to avoid duplicating this logic in the
compiler, libc++ and libc++abi.

Reviewers: EricWF

Subscribers: mgorny, christof, dexonsmith, libcxx-commits, davide

Differential Revision: https://reviews.llvm.org/D53028

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@344191 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed