core.sys.windows.com.ComObject apparently has wrongly laid out Vtable

[Carl Sturtivant]

Now here's the new ComObject class, identical to that in druntime 
apart from the necessary `com.` prefix due to the static import 
of `core.sys.windows.com`, except that I declared the class 
extern(C++).
```D
import com = core.sys.windows.com;
import windows = core.sys.windows.windows;

import core.atomic;


extern(C++) class ComObject : com.IUnknown
{
     HRESULT QueryInterface(const(com.IID)* riid, void** ppv)
     {
         if (*riid == com.IID_IUnknown)
         {
             *ppv = cast(void*)cast(com.IUnknown)this;
             AddRef();
             return S_OK;
         }
         else
         {   *ppv = null;
             return com.E_NOINTERFACE;
         }
     }

     ULONG AddRef()
     {
         return atomicOp!"+="(*cast(shared)&count, 1);
     }

     ULONG Release()
     {
         LONG lRef = atomicOp!"-="(*cast(shared)&count, 1);
         if (lRef == 0)
         {
             // free object

             // If we delete this object, then the postinvariant 
called upon
             // return from Release() will fail.
             // Just let the GC reap it.
             //delete this;

             return 0;
         }
         return cast(ULONG)lRef;
     }

     LONG count = 0;             // object reference count
}
```
So this ComObject inherits from the druntime interface IUnknown 
and according to the docs therefore has extern(System) as its 
default for methods, which is extern(Windows) here.