[llvm] [GlobalISel] Fix [SU]SUBO combine (PR #116998)

[Amara Emerson via llvm-commits]

aemerson wrote:

> Our documentation describes the carry-in and -out as s1. It cannot be a target dependent infinity: https://llvm.org/docs/GlobalISel/GenericOpcode.html#g-uadde-g-sadde-g-usube-g-ssube

I think that just mirrors what the langref says for overflow intrinsics, which basically say that output is a bit indicating a carry. The carry bit is IMO a boolean which we need to legalize into whatever representation the target needs for the boolean. Am I misunderstanding something here?

https://github.com/llvm/llvm-project/pull/116998