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

[Paul Osmialowski via cfe-commits]

pawosm-arm wrote:

> We should probably also handle `no-infs-fp-math` to save the next person the trouble.

I'd leave it to a separate PR, as this one has a specific story behind the proposed change, anything extra would go beyond it.

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