[llvm] [ValueTracking] Take into account whether zero is poison when computing CR for `ct{t,l}z` (PR #122548)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

Motivation? The opt result will not be improved since it has been handled in ConstantRange::ctlz/cttz.


https://github.com/llvm/llvm-project/pull/122548