https://issues.dlang.org/show_bug.cgi?id=21531

          Issue ID: 21531
           Summary: dtoh: Forward-referencing issue wrt. globals of custom
                    types
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody@puremagic.com
          Reporter: kinke@gmx.net

In current frontend.h, we have:

```
[...]
struct Global;
[...]
extern Global global;

struct Loc
{
    [...]
    const char* toChars(bool showColumns = global.params.showColumns, uint8_t
messageStyle = static_cast<uint8_t>(global.params.messageStyle)) const;
    [...]
};
```

The `Global` struct declaration follows later but is required before `Loc::toChars()` and its default parameter values.

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