[clang] [CIR][SPIR-V] Set spir_kernel calling convention for AMDGCN-flavored HIP kernels (PR #214246)

[Arseniy Obolenskiy via cfe-commits]

aobolensk wrote:

> > Hm, from what I can see setTargetAttributes runs every time when `cir::FuncOp` is being created (in both cases when we handle both declaration and definition) for all functions (incl. CXX methods and so on).
> > Or should we rather mimic the classic codegen fully? Meaning that we implement `setCUDAKernelCallingConvention` and so on
> 
> I would prefer to mimic the structure of classic codegen as fully as is practical. It makes keeping them synchronized easier if something changes in classic codegen. I guess this applies to the existing code that sets the calling convention for OpenCL as well, though I don't know where that should have been done.

Aligned the paths at this point by implementing setCUDAKernelCallingConvention and other necessary helpers

https://github.com/llvm/llvm-project/pull/214246