[llvm] Reland [llvm] Add support for llvm IR atomicrmw fminimum/fmaximum instructions (PR #137701)

[Jonathan Thackray via llvm-commits]

jthackray wrote:

The only change different from the original (now reverted) is updating `llvm/test/TableGen/GlobalISelCombinerEmitter/match-table-cxx.td` because this change:
```
commit c792b25e4
Author: Pierre van Houtryve <[pierre.vanhoutryve at amd.com](mailto:pierre.vanhoutryve at amd.com)>
Date:   Fri 12:10 +0200

    [GlobalISel] Add `combine` action for C++ combine rules (#135941)
```
landed just before I merged (and I hadn't rebased over the weekend).

https://github.com/llvm/llvm-project/pull/137701