[Issue 18645] DMD segmentation fault

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=18645

--- Comment #2 from Mihails Strasuns <mihails.strasuns.contractor at sociomantic.com> ---
Even more reduced case:

```
immutable INIT = 42;

enum A
{
    x = INIT,
    y
}
```

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