[llvm] AMDGPU: Add tonearest and towardzero roundings for intrinsic llvm.fptrunc.round (PR #104486)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> > Yes. You just need an SDNodeXForm to modify the value
> 
> What about a rounding mode that is not supported, such as "round.tonearestaway"?
> 

You can use a TImmLeaf predicate on the immediate value (which can also combine the xform)

https://github.com/llvm/llvm-project/pull/104486