[Issue 22981] Another forward reference bug involving a string mixin

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=22981

--- Comment #10 from Basile-z <b2.temp at gmx.com> ---
looks like enum being integral is assumed too early ;)

for example if you change the infered type of S.a

```
enum E { e1 = S.a }

struct S
{
    E e;
    enum a = 123; // vs enum a = "string"
}     
```

no problems anymore

--