[llvm] [ConstantFolding] Fold vector reduce `fmax` and `fmin` intrinsics (PR #143904)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Do we are about SNANs in the default FP environment?

Yes, you must for minnum and maxnum because it's a total value change, not a question of quiet or not 

https://github.com/llvm/llvm-project/pull/143904