[llvm] [AMDGPU] Implement "non-av" semantics using metadata (PR #199489)

[Sameer Sahasrabuddhe via llvm-commits]

ssahasra wrote:

> Don't see any issues with this. You could also add a test that combines the synchronize-as metadata with the av metadata, for applicable areas.

Done.

https://github.com/llvm/llvm-project/pull/199489