x/vulndb: derived symbols missing for reference via closure

[neild]

In https://go.dev/cl/415800, we list the handleMessage symbol.

handleMessage is called by handle, and handle is referenced--but not called--by MakeProtocols. We'd expect MakeProtocols to appear in the derived symbols after running vulnreport fix, but it does not, probably because it doesn't actually call handle.

[zpavlinovic]

An old issue, but do we still need a fix for this?

If MakeProtocols is not (transitively) calling handleMessage, then it won't appear as a derived symbol. There is currently no easy way to change that unfortunately.