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

[Krzysztof Drewniak via llvm-commits]

krzysz00 wrote:

@jayfoad I was trying to avoid explicitly saying there's a hardware bug in the patch because I wasn't sure legal would like it.

But I'm open to going to the clause length bug feature like you proposed if you think it'd be cleaner - I was also unsure if, for example, we'd end up with future hardware that allows for a clause length of 64 (instead of the old 63).

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