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

[Sameer Sahasrabuddhe via llvm-commits]

ssahasra 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?? When lowering calls, we do glue stuff onto the actually call instruction. Now we also need to glue the convergence token to the same call. The existing attempt happily created a second glue operand, and this change fixes that to have a single glue operand which could itself have a chain of glued operands.

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