[llvm] IR: de-duplicate two CmpInst routines (NFC) (PR #116866)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

I think it might make more sense to drop the methods on CmpInst instead? getSignedPredicate and getUnsignedPredicate only make sense for icmps, so I'd expect them to be on ICmpInst only. Or does that make usage awkward somehow?

https://github.com/llvm/llvm-project/pull/116866