[llvm] [AArch64] Stop reserved registers from being saved in prolog/epilog (PR #138448)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

Can you add some tests? I have a feeling this has come up before and there were edge cases to worry about, but don't know the history.

https://github.com/llvm/llvm-project/pull/138448