[D1] fix issue 13521 : -di ignores variable shadowing

https://issues.dlang.org/show_bug.cgi?id=13521

```D
void f()
{
    int i;
    { int i; }
}
```

```
$ dmd1 -c shadow.d
shadow.d(4): Deprecation: shadowing declaration shadow.f.i is deprecated
$ dmd1 -c -di shadow.d
```