[compiler-rt] [Compiler-rt] Add AArch64 routines for __arm_agnostic("sme_za_state") (PR #120059)

[Kerry McLaughlin via llvm-commits]

https://github.com/kmclaughlin-arm approved this pull request.

I've added two more minor comments, but otherwise this LGTM.

https://github.com/llvm/llvm-project/pull/120059