[llvm] [AMDGPU] Emit a waitcnt instruction after each memory instruction (PR #68932)

[Jay Foad via llvm-commits]

jayfoad wrote:

What's the reason for this?

Do we really need both this option and the existing `-amdgpu-waitcnt-forcezero`?

https://github.com/llvm/llvm-project/pull/68932