Switch libunwind-unit-tests to unit_test:true and add the lib for host-unit-tests am: 8d1b285f94

Original change: https://android-review.googlesource.com/c/platform/external/libunwind/+/1582278

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I304a248b26d981277ca12f7ace5b9f82da5408fb