[clang] [llvm] [AMDGPU] Add OpenCL-specific fence address space masks (PR #78572)

[Matt Arsenault via cfe-commits]

arsenm wrote:

> I'm now wondering if adding a new builtin is needed at all, or if it should just be part of the original builtin? It's an additive change.

Maybe?

> 
> Should we also rename the MMRA to `amdgpu-fence-as` (remove OpenCL from the name) ?
> 

I definitely do not want to maintain any language names in anything 


https://github.com/llvm/llvm-project/pull/78572