Enum that references its own members doesn't pass through onSymbol
I've got an enum that looks a bit something like this:
```
enum {
    _ONE,
    _TWO,
    _MAX = _TWO,
    _MORE
}
```
The first `_TWO` gets renamed to `TWO` with a rule in `onSymbol`, but `_MAX = _TWO` gets renamed to `MAX = _TWO` which obviously fails. The value of `_MORE` would also be 4 in the Nim code, not sure what the behaviour of C enums are in this case though, but I'm not sure if that's right.