[PATCH 6/6] [RESEND] drm/amdgpu: work around llvm bug #42576

[Nick Desaulniers]

> Apparently this bug is still present in both the released clang-9
> and the current development version of clang-10.
> I was hoping we would not need a workaround in clang-9+, but
> it seems that we do.

I think I'd rather:
1. mark AMDGPU BROKEN if CC_IS_CLANG. There are numerous other issues building
   a working driver here.
2. Fix the compiler bug.