[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:

https://github.com/llvm/llvm-project/pull/142199 should ideally fix this for AMDGPU, then this should be a small change + test.

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