Wrong ABI size for imported enum
### Description

Importing `enum` into Nim is broadly a bad idea given the semantic differences, but it's done anyway - when doing so, Nim should respect C `enum` ABI rules - in particular, an enum is sized as `cint` ~~by default~~ most of the time but not always.

```
type X {.importc: "someenum".} = enum
  ...
```

Failing to do so leads silent miscompiles (and fails `-d:checkAbi`)

### Nim Version

devel

### Current Output

_No response_

### Expected Output

_No response_

### Known Workarounds

_No response_

### Additional Information

_No response_