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

[Oscar Smith via llvm-commits]

oscardssmith wrote:

I've started looking into writing more intensive tests for this, (see llvm/test/CodeGen/RISCV/rv64zbc+zbkb-intrinsic.ll for a currently broken test for the 128 bit clmul. That said, is there any specific places where these tests should go? From brief reading online and looking through the test infrastructure, it doesn't look like there's a standardized place for this sort of testing (I very well might be missing something though.)

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