cOverride content gets injected multiple items, once for each following cImport
Hello,

This is just a continuation of our discussion on https://gitter.im/nimterop/Lobby?at=5dbc3211bbdf5f17b420b24d.

With a pseudocode like:

```
cOverride:
  type
    Foo = enum
      fooOne
      fooTwo
..
cImport(..)
cImport(..)
cImport(..)
..
```

, I get an error like:

> ../nim/1.0.0/lib/core/macros.nim(562, 3) Error: redefinition of 'Foo'; previous declaration here: ../nim/1.0.0/lib/core/macros.nim(562, 3)

---

**OS**: RHEL 6.8
**Nim version**: 1.0.0
**nimterop version**: 0.3.2