[libunwind] [libunwind] Call `__arm_za_disable` before entering EH (PR #160905)

[Benjamin Maxwell via cfe-commits]

MacDue wrote:

Does any libunwind reviewer have an opinion on this approach? If not, we plan to land this soon. An alternative approach would be to re-implement `__arm_za_disable` in `libunwind` (tested here: https://github.com/llvm/llvm-project/pull/165451), but it would be nice to avoid that. 

(Ping @llvm/reviewers-libunwind)

https://github.com/llvm/llvm-project/pull/160905