Rollup merge of #143395 - Urgau:llvm-fallback-minimum-maximum, r=tgross35

Always use the pure Rust fallback instead of `llvm.{maximum,minimum}`

While llvm/llvm-project#142170 was merged, it was reverted and next attempt (llvm/llvm-project#140193) at fixing the LLVM implementation seems to have stall, so let's reverted back to pure Rust with the LLVM codegen.

cc [#t-compiler/llvm > &rust-lang#96;llvm.minimum&rust-lang#96;/&rust-lang#96;llvm.maximum&rust-lang#96; issues @ 💬](https://rust-lang.zulipchat.com/#narrow/channel/187780-t-compiler.2Fllvm/topic/.60llvm.2Eminimum.60.2F.60llvm.2Emaximum.60.20issues/near/527044712)

Fixes rust-lang/rust#141087
r? `@tgross35`

Author: jhpratt