[llvm] [SDAG] Fix fmaximum legalization errors (PR #142170)

[YunQiang Su via llvm-commits]

wzssyqa wrote:

> Same issue exists for fmaximumnum. I have a fix for that, but #139237 needs to land first.

I have another proposal with `FP_ROUND`: ROUND to FP32 first.

https://github.com/llvm/llvm-project/pull/142170