[llvm] IR: Add verifier plugins for intrinsic verification (PR #159415)

[Nicolai Hähnle via llvm-commits]

nhaehnle wrote:

> It would be an improvement to just split this out into the separate files without placing it in the backends

What really motivated this is that I was exploring new intrinsics for which verification could benefit from some shared defines and helper functions, and there really isn't a great place to put those. I thought of putting them into Target/AMDGPU/Utils, which is what motivated this change (where just splitting out into a separate file is insufficient).

I see your point about `llvm-as` though -- it'd be good for that to not depend on CodeGen.

As for what the alternatives are... it seems a lot of stuff just ends up getting dumped into Support (like NVPTXAddrSpace.h or DXILABI.h). Perhaps that stuff should go under IR/${target}/ directories instead?

https://github.com/llvm/llvm-project/pull/159415