[clang] [RFC][Clang][AMDGPU] Emit only delta target-features to reduce IR bloat (PR #176533)

[Stanislav Mekhanoshin via cfe-commits]

rampitec wrote:

> > I like this. I agree we probably do not need an option, this is just the extra code.
> 
> aka we don't want to test whether we fill the feature map correctly? It is a separate map from the one defined in `AMDGPU.td`.

Probably not. I have to update these tests more often than I actually catch anything useful form them.

https://github.com/llvm/llvm-project/pull/176533