[llvm] [AArch64] Lower alias mask to a whilewr (PR #100769)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

Thanks - I have looked at the whilewr instruction in the past and I was worried the semantics would make them a bit difficult. These seem to check out just fine though.

https://github.com/llvm/llvm-project/pull/100769