[llvm] [AArch64] Use isKnownNonZero to optimize eligible compares to cmn (PR #96349)

[David Green via llvm-commits]

davemgreen wrote:

OK. If that has succeeded and a bootstrap also does OK, then if you can add some more tests for various ccmn cases we can get this in.

https://github.com/llvm/llvm-project/pull/96349