[clang] [llvm] [Transforms][Utils][PromoteMem2Reg] Propagate nnan flag on par with the nsz flag (PR #114271)

[Paul Osmialowski via cfe-commits]

pawosm-arm wrote:

> > I've rebased my PR so this branch could also contain phase-ordering test for vectorizing predicated selects introduced by commit [577c7dd](https://github.com/llvm/llvm-project/commit/577c7dd7cc4c5a9f62f9654cfa30ee9d55709426)
> 
> Do I understand correctly that this PR doesn't change the PhaseOrdering test because the motivating issue was already addressed by [0f91944](https://github.com/llvm/llvm-project/commit/0f919444adfa74b46df50aa2da12e7137c23a02c)?

Yes, the original problem that I've faced could be addressed various ways, and 0f91944 indeed fixes it too. Yet we see a value in the change proposed here too hence a good reason for merging it.

https://github.com/llvm/llvm-project/pull/114271