[llvm] [AArch64] Take cmn into account when adjusting compare constants (PR #97774)

[via llvm-commits]

AtariDreams wrote:

Another note, it would be nice if we could merge cmps like cmp x1, #0, and cmn x1, #1 if the values tested for 100% overlap, but I don't know if that should be done here, or somewhere else.

https://github.com/llvm/llvm-project/pull/97774