is_not_zero: ensure equality test has exactly matching types

[smowton]

This is required to eliminate base_type_eq in #4056

[kroening]

It bugs me a bit that we basically have to do this on every usage of from_integer.
Are there views on giving a namespace to from_integer?

[allredj]

✔️
Passed Diffblue compatibility checks (cbmc commit: 0225d20).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/100752679

[kroening]

Oh, and an alternative would be to stuff the subtype of the enum into the tag type.

[tautschnig]

Maybe from_integer shouldn't support enums? One could always use zero_initializer instead.

[smowton]

So, merge this and refactor later, or...?

[kroening]

Merge now, I'd say, but let's keep thinking about it.
@tautschnig zero_initializer can do it because it gets a namespace.

[tautschnig]

I have reviewed the 20 lines preceding each use of from_integer - #4178 was the only case that seemed left to handle, with only four or so cases (among more than 900) doing anything about enums.

[kroening]

Many thanks; those four are not likely worth the tweak to the signature of from_integer.