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

[Jun Wang via llvm-commits]

jwanggit86 wrote:

The waitcnt insertions by the SIInsertWaitcnt pass is not controlled by any command-line option. In other words, there's no command-line option to enable/disable the insertions. There is one option, however, i.e., `--amdgpu-waitcnt-forcezero`, when used, would force all the inserted waitcnt to be "waitcnt 0". On the other hand, the command-line option for this feature is an enable/disable type of option. So, while it's possible to create a combined option, using a separate option also makes sense. Do we generally try to avoid creating new command-line options?

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