[clang] [llvm] [AMDGPU] Emit a waitcnt instruction after each memory instruction (PR #79236)

[Pierre van Houtryve via cfe-commits]

https://github.com/Pierre-vh approved this pull request.

LGTM, but wait for @t-tye or @jayfoad to approve as well

https://github.com/llvm/llvm-project/pull/79236