"Internal error looking up a definition" when assigning an enum a value from a variable

This works:

```
fn main() {
    enum Stuff {
        Bar = 100
    }

    log(error, Bar);
}
```

But this doesn't:

```
fn main() {
    let foo = 100;

    enum Stuff {
        Bar = foo  // error: internal error looking up a definition
    }

    log(error, Bar);
}
```
