[llvm] [NVPTX] Rework and cleanup FTZ ISel (PR #146410)

[Alex MacLean via llvm-commits]

AlexMaclean wrote:

> > This change cleans up DAG-to-DAG instruction selection around FTZ and SETP comparison mode. Largely this is non-functional though support for {sin.cos}.approx.ftz.f32 is added.
> 
> Is "Non-functional" as in "does not work" or did you mean "no functional changes" ?

It's the latter, I've updated the description for clarity. 

https://github.com/llvm/llvm-project/pull/146410