[libunwind] [libunwind] Fix problems caused by combining BTI and GCS (PR #102322)

[Daniel Kiss via cfe-commits]

https://github.com/DanielKristofKiss approved this pull request.

Thanks!
LGTM with a NIT.
Please wait for someone from the unwind group to ack it too.

https://github.com/llvm/llvm-project/pull/102322