[clang] [llvm] [SPIRV] GPU intrinsics (PR #131190)

[Jon Chesterfield via llvm-commits]

JonChesterfield wrote:

I've dropped the clang headers part from this patch, rewritten to elide the grid intrinsic and moved the test. Matt suggested llvm.simt as the prefix which I like very much more than llvm.gpu but the rename is probably going to take a moment.

Turns out I do need to update the amdgpu attributor pass to know about the new names which is upsetting but fine.

https://github.com/llvm/llvm-project/pull/131190