Moved ICOM_THIS_MULTI definition out of objbase.h and into the files
that use it.

diff --git a/dlls/ole32/compobj_private.h b/dlls/ole32/compobj_private.h
index d69d179..ee4e33b 100644
--- a/dlls/ole32/compobj_private.h
+++ b/dlls/ole32/compobj_private.h
@@ -189,4 +189,6 @@
 APARTMENT* COM_CreateApartment(DWORD model);
 HWND COM_GetApartmentWin(OXID oxid);
 
+#define ICOM_THIS_MULTI(impl,field,iface) impl* const This=(impl*)((char*)(iface) - offsetof(impl,field))
+
 #endif /* __WINE_OLE_COMPOBJ_H */