[llvm] AMDGPU: Ensure both wavesize features are not set (PR #159234)

[Jay Foad via llvm-commits]

jayfoad wrote:

> This breaks the assembler test which enables both, but this
> behavior is not really useful.

It's useful for assembling a single source file containing wave32 and wave64 code. This is common in graphics where you can have a single pipeline containing two shaders, like a vertex shader using wave32 and a pixel shader using wave64.

https://github.com/llvm/llvm-project/pull/159234