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

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

>  I wonder why this has such a small impact on llvm-opt-benchmark?

I guess it will become more useful after we let `makeExactICmpRegion` to leverage samesign as well.

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