[llvm] [SDAGBuilder] Fix incorrect fcmp+select to minnum/maxnum transform (PR #184590)

[Ralf Jung via llvm-commits]

RalfJung wrote:

>  we must convert to minimumnum/maximumnum instead.

Even that can still alter NaN payloads as per the usual NaN rules, whereas select exactly returns one of the operands, doesn't it? So this still seems like an incorrect transform?

https://github.com/llvm/llvm-project/pull/184590