[llvm] [IR] Add llvm `clmul` intrinsic (PR #140301)

[Min-Yih Hsu via llvm-commits]

https://github.com/mshockwave commented:

> SelectionDag tests to show that the fallbacks implemented here are correct

I guess you were referring to checking whether the expansion logics is correct. In that case you can add a RISC-V test without `zbc` in  `-mattr` (so that it won't use the `clmul` instruction) and check the emitted assembly.

https://github.com/llvm/llvm-project/pull/140301