[llvm] [AArch64] Optimize CBZ wzr and friends. (PR #161508)

[David Green via llvm-commits]

davemgreen wrote:

> Would it make sense to also check for `cb.{eq,ne} {x,w}zr, #0`? Not sure if we'd ever codegen that though.

I've not seen that come up, but it's fairly early for it so far. It might come up, we can expand this to handle them in the future if this works out OK.

https://github.com/llvm/llvm-project/pull/161508