[llvm] [AMDGPU] Make maximum hard clause size a subtarget feature (PR #81287)

[Jay Foad via llvm-commits]

https://github.com/jayfoad commented:

Personally I would have gone with a new `HasClauseLengthBug` (or similar) feature, but I guess this approach is OK too.

I do think we need a brief comment (maybe on the definition of `FeatureMaxHardClauseLength32`) explaining _why_ clause length is limited to 32 on some subtargets, i.e. saying that it is a workaround for some bug rather than being something that is documented in the ISA manuals.

https://github.com/llvm/llvm-project/pull/81287