[llvm] [NVPTX] Constant-folding for f2i, d2ui, f2ll etc. (PR #118965)

[Lewis Crawford via llvm-commits]

LewisCrawford wrote:

Adding @nikic and @MDevereau for feedback on whether ConstantFolding.cpp is still the right place to add target-specific intrinsic folding like this. 

Is it ok to keep going as-is, or do we want to split out either all targets (or just the NVVM intrinsics) into a separate target-specific constant-folding files?

I have several draft patches to add even more NVVM intrinsics here, so this patch is a proof-of concept to get feedback about where is best to put this code.

https://github.com/llvm/llvm-project/pull/118965