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

Fri May 16 12:25:55 PDT 2025

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

This is the generic version of `int_x86_pclmulqdq`, and `riscv_clmul` as discussed in https://discourse.llvm.org/t/rfc-carry-less-multiplication-instruction/55819/26, (and will allow implementations for powerpc and aarch64 backends that have this instruction but no backend intrinsic).

So far I have only hooked this up for the RISCV backend, but the x86 backend should be pretty easy as well.

This is my first LLVM PR, so please tell me everything that I've messed up.

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