[llvm] GlobalISel: Use G_UADDE when narrowing G_UMULH (PR #97194)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> The same would be combining from more primitives ops into G_UADDE.

This is an argument against having any optimizations. Most optimizations are of the form take-simpler-instructions and form more-complex instructions. 

https://github.com/llvm/llvm-project/pull/97194