[llvm] [DAG] SelectionDAG::canCreateUndefOrPoison - add ISD::SCMP/UCMP handling + tests (PR #154127)

[via llvm-commits]

AZero13 wrote:

> > Can you add it in the same category as umax amd umin in ir and globalisel too since we are here already?
> 
> Is the same change that RKSimon suggested?

Yeah

https://github.com/llvm/llvm-project/pull/154127