[llvm] [TableGen] Handle RegClassByHwMode in AsmWriter (PR #171264)

[Alexander Richardson via llvm-commits]

arichardson wrote:

I used https://github.com/llvm/llvm-project/pull/171265 to test that the output compiles (but it doesn't look like it generates sensible asm for AMDGPU).

https://github.com/llvm/llvm-project/pull/171264