[llvm] [CVP]: Fold `icmp eq X, C` to `trunc X to i1` if C=2k+1 and X in [2k, 2k+1] (PR #83829)

[via llvm-commits]

AtariDreams wrote:

<img width="565" alt="Screenshot 2024-03-29 at 3 24 06 PM" src="https://github.com/llvm/llvm-project/assets/83477269/60b0ba64-0c62-4d37-8ac2-014225baca5d">
While we are at it, should we remove the scalar restriction for the fold here as well in InstCombineCompares?

https://github.com/llvm/llvm-project/pull/83829