[llvm] [AMDGPU] Respect existing glue when lowering convergence tokens (PR #90834)

[Jay Foad via llvm-commits]

jayfoad wrote:

> > I guess no nodes actually require this yet. Are you expecting any? Or is this just defensive programming?
> 
> What is "this" in this context??

"This" meant "this patch". I was trying to work out what kind of patch this is. Does it fix a bug? Why is there no test case?

https://github.com/llvm/llvm-project/pull/90834