[llvm] [mlir] Add llvm::min/max_element and use it in llvm/ and mlir/ directories. (PR #84678)

[Justin Lebar via llvm-commits]

jlebar wrote:

Hm, I got a bazillion buildbot errors from this.  Weird, because I did test the build locally before I pushed it.

Back when we used phab there was a bot that built PRs before they were checked in; do we not have that anymore?

https://github.com/llvm/llvm-project/pull/84678