[llvm] [GlobalIsel] Add G_SCMP and G_UCMP instructions (PR #98894)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

Next steps could be:
* Teach the IRTranslator to translate the intrinsics to G_[US]CMP.
*  Add `lower` methods for default implementations. 
* Add to targets:
```
getActionDefinitionsBuilder({G_SCMP, G_UCMP})
  .lower();
```

https://github.com/llvm/llvm-project/pull/98894