[llvm] [LegalizeDAG] Optimize CodeGen for `ISD::CTLZ_ZERO_UNDEF` (PR #83039)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

The lldb timeout is an intermittent fail - nothing to do with your patch.

Not sure about the bolt regression, but I think this is safe to commit - the bolt team are pretty good at fixing anything that comes up due to their project dependencies (you're not expected to fix everything yourself).

https://github.com/llvm/llvm-project/pull/83039