[llvm] [AMDGPU][GlobalISel] Handle constant i32 ballot on wave64 (PR #205536)

[Manuel Carrasco via llvm-commits]

mgcarrasco wrote:

I understand that the tricky part is knowing what the expected behavior should be. This is another option to consider, if it makes sense: could this be treated as legal IR but UB? In that scenario, anything could be emitted, while preventing the original crash.

https://github.com/llvm/llvm-project/pull/205536