[llvm] [JumpThreading] Convert `s/zext i1` to `select i1` for further unfolding (PR #89345)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

@dtcxzyw Can you please test this? I'm not sure whether this does more damage than good...

https://github.com/llvm/llvm-project/pull/89345