Add libcxxabi_headers filegroup am: a07162d9ed

Original change: https://android-review.googlesource.com/c/platform/external/libcxxabi/+/2853447

Change-Id: Ia0e446ee7453fe04af2da1649861d9a66b7889db
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>