[Issue 23185] New: importC: anonymous struct inside __builtin_offsetof doesn't compile

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23185

          Issue ID: 23185
           Summary: importC: anonymous struct inside __builtin_offsetof
                    doesn't compile
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: blocker
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: ryuukk.dev at gmail.com

The following code doesn't compile:

```
void test()
{
    int a = __builtin_offsetof(struct { int a;}, a);
}
```

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