[clang] clang/AMDGPU: Set amdgpu-max-num-workgroups to disable Y/Z by default (PR #119009)

[Matt Arsenault via cfe-commits]

arsenm wrote:

So this is wrong. It was correct for openmp. Is there a language version we check can where 3d grids were introduced? 

https://github.com/llvm/llvm-project/pull/119009