[llvm] [SystemZ] Mark fminimumnum/fmaximumnum as legal (PR #184595)

[Ulrich Weigand via llvm-commits]

uweigand wrote:

> > The only difference between our mode M=4 and `minimumNumber` is that M=4 may return an input SNaN as-is, without changing it to the corresponding QNaN. We do not have a mode that matches `minimumNumber` precisely. Does this matter, given that this is a non-strict IR opcode?
> 
> This is fine, non-constrained operations are explicitly allowed to omit NaN canonicalization.

I see.   This patch certainly LGTM then.

https://github.com/llvm/llvm-project/pull/184595