[llvm] [PPC] Add custom lowering for uaddo (PR #110137)

[Eli Friedman via llvm-commits]

https://github.com/efriedma-quic commented:

Looks fine from my side, but I don't really have much context for PPC instruction sets, so a PPC expert should also look at it.

https://github.com/llvm/llvm-project/pull/110137