[llvm] [ConstraintElim] Simplify `sadd_with_overflow` if A and B have different signs (PR #135784)

[Nikita Popov via llvm-commits]

nikic wrote:

I'm not sure this is really a useful optimization. I'd expect that for typical usages the sign will be the same. Looks like the llvm-opt-benchmark run did not have any hits either (https://github.com/dtcxzyw/llvm-opt-benchmark/pull/2274).

https://github.com/llvm/llvm-project/pull/135784