[llvm] [InstCombine] Preserve the nsw flag for (X | Op01C) + Op1C --> X + (Op01C + Op1C) (PR #94586)

[via llvm-commits]

csstormq wrote:

> Please always provide alive2 proofs for InstCombine changes, see https://llvm.org/docs/InstCombineContributorGuide.html#proofs.
> 
> The transform as implemented is incorrect: https://alive2.llvm.org/ce/z/pEk7wC

Alive2 Proof: https://alive2.llvm.org/ce/z/CRKtkU

https://github.com/llvm/llvm-project/pull/94586