[llvm] RFC: [AMDGPU] Check subtarget features for consistency (PR #86957)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> > For the purpose of this change, it's probably OK to ignore it.
> 
> Like this? I just added `not` to the failing `RUN` line.

I think the current "unknown processor" behavior of warn and proceed is utter nonsense. However, this is a different case to codegening the none/default/generic processor 

https://github.com/llvm/llvm-project/pull/86957