[clang] [llvm] [AMDGPU] Extend __builtin_amdgcn_sched_group_barrier to support rules. (PR #85304)

[Matt Arsenault via cfe-commits]

https://github.com/arsenm commented:

I don't understand how anyone is supposed to use this. This is exposing extremely specific, random low level details of the scheduling. Users claim they want scheduling controls, but what they actually want is the scheduler to just do the right thing. We should spent more energy making the scheduler sensible by default, instead of creating all of this complexity.

If we're going to have something like this, it needs to have predefined macros instead of expecting reading 

https://github.com/llvm/llvm-project/pull/85304