[llvm] [AMDGPU] Conditionally enable DAG combines for fminimum/fmaximum (PR #81584)

[Jay Foad via llvm-commits]

jayfoad wrote:

Other possible approaches:
- implement legalization for fminimum3/fmaximum3
- only do the combine post-legalization

I'm not sure which approach is best.

https://github.com/llvm/llvm-project/pull/81584