[llvm] [AArch64][ISel] Add lowering for fixed-width `cttz` intrinsic (PR #190988)

[David Green via llvm-commits]

davemgreen wrote:

Yep - if there is no simple way to make a i64 clz then it makes sense to leave that one out.

Can you remove the extra debug code left in the patch?

https://github.com/llvm/llvm-project/pull/190988