Track the terminating vs. non-terminating code paths for a given node

[lupino3]

A node can be both terminating and non-terminating, depending on how it's invoked.

If it's reached via goto or nested from a node that would have been terminating, it's terminating for that code path. But if it's reached via call from a non-terminating node, it's not terminating.

It would be nice to surface this information somehow. The easiest option might be a warning, not sure how to actually represent this case in the call graph.