[llvm] [ISel] Introduce llvm.clmul intrinsic (PR #168731)

[Piotr Fusik via llvm-commits]

https://github.com/pfusik commented:

On RISC-V, we should also select `vclmul[h]`. I'm okay with that being done in a subsequent PR.

https://github.com/llvm/llvm-project/pull/168731