[llvm] [KnownBits] Make nuw and nsw support in computeForAddSub optimal (PR #83382)

[via llvm-commits]

goldsteinn wrote:

@nikic think compile time issue has been resolved:
https://llvm-compile-time-tracker.com/compare.php?from=ae76dfb74701e05e5ab4be194e20e49f10768e46&to=04e24f0c7903a2ffa06a9c30f952796fa1527157&stat=instructions%3Au

https://github.com/llvm/llvm-project/pull/83382