[llvm] [AArch64][SME] Don't use glue for call lowering's SMSTART. (PR #68630)

[Sander de Smalen via llvm-commits]

https://github.com/sdesmalen-arm commented:

> I've been working on LLVM for over a decade now, and I've still yet to understand what Glue is, so I'm not sure if this change is correct.

The meaning of `Glue` is that it directs the SelectionDAG scheduler to schedule a node straight after another node, without anything scheduled in between. In contrast, a `Chain` just specifies that A needs be scheduled before B, it still allows other unchained nodes to be scheduled in between. Glue is stronger in that respect.

https://github.com/llvm/llvm-project/pull/68630