[llvm] [Legalizer] Expand fmaximum and fminimum (PR #67301)

[Qiu Chaofan via llvm-commits]

ecnelises wrote:

> I still think we should avoid using is_fpclass here

`fgetsign` is not legal or expanded in every targets. To support comparison of signed zeros, should we duplicate similar logic of is_fpclass expansion? (bitcast them to int and do int comparison)

https://github.com/llvm/llvm-project/pull/67301