boolbvt: convert_with now does struct_tag and union_tag types

[kroening]

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[tautschnig]

Ok, but how did you notice? Do we know this is the last one?

[kroening]

@tautschnig There are currently a lot of bugs like this one hidden behind the fact that symbol types and struct and union tags are expanded during symbolic simulation.

Once we stop that expansion we should see these.

[tautschnig]

I was guessing as much; as a reviewer, it's would be nice to have some info like "fixes N tests when not expanding tags during symex." (And maybe "Y tests remaining to be debugged.")

[allredj]

Passed Diffblue compatibility checks (cbmc commit: dbec311).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/86674798