[llvm] [Offload] Allow setting null arguments in olLaunchKernel and fix amdgpu handling for empty kernel arguments (PR #141958)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> I've pushed up an additional change to this PR; the thing I was debugging originally was that the amdgpu driver would throw an error if a function was being called with no arguments at all.
> 
> However, more digging has revealed that even if you build a kernel with no arguments at the C level, when compiled at O0 a number of "hidden" arguments are added. The new change compiles the noargs.cpp test with O3 and fixes amdgpu to pass.
> 
> Not sure if the fixes to amdgpu are worth moving into their own MR or not though.
> 
> Also, I checked: `kernarg_address` in `hsa_kernel_dispatch_packet_t` may be `NULL`.

Oh yeah, I was going to fix that. There's alignment issues as well.

https://github.com/llvm/llvm-project/pull/141958