[llvm] [KnownBits] Simplify optimality checking in unit tests. NFC. (PR #89368)

[Nikita Popov via llvm-commits]

https://github.com/nikic approved this pull request.

IIRC this is adopted from the ConstantRange implementation where we have a lot of operations that are only optimal for some inputs (e.g. only non-wrapping ranges). If we don't need something this fine-grained for KnownBits, a plain boolean is of course better...

https://github.com/llvm/llvm-project/pull/89368