[llvm] [ConstantRange] Expand makeAllowedICmpRegion to use samesign to give tighter range (PR #174355)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> What do you all think? Which version would you prefer we continue with?

The latest compile-time result looks good: https://github.com/dtcxzyw/llvm-opt-benchmark-nightly/pull/159
https://llvm-compile-time-tracker.com/compare.php?from=91c0fdfe13928838864d9618ea28dcbe9a112b8c&to=23c6009858d292b56c98add90c60767ef1b140a8&stat=instructions:u

https://github.com/llvm/llvm-project/pull/174355