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

[David Green via cfe-commits]

davemgreen wrote:

This patch should help with the performance in other ways than the motivating case from #113686 (the creating of fmin/fmax is one of them). Those could probably be fixed in other ways, and my understanding was that there was a long term goal to move away form the function level FMF attributes. But this should help performance in a fairly generic way.

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