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

[Matt Arsenault via llvm-commits]

arsenm wrote:

> One thing this makes me wonder is why we're not preferring libcall legalization for scalar fmaximum. The generated code is quite complex and probably not better than using a libcall.

Are there even libcalls? We unfortunately don't know the target runtime versions and these are really new calls 

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