[llvm] [GISel] handle CTTZ in `computeKnownBits` (PR #181474)

[Aayush Sabharwal via llvm-commits]

AayushSabharwal wrote:

Thanks for the review! In case the approval is an indication to merge (the Contributing guidelines indicate it is) I do not have merge permissions, and thus someone will need to do it for me.

https://github.com/llvm/llvm-project/pull/181474