Q_NAMESPACE does not compile even if QtGlobal is included

If `Q_NAMESPACE` is used, the moc compilation fails with

'Q_NAMESPACE' does not name a type

Unless `#include <QtCore/QObject>` is added. This isn't due to the fact that QObject define the macro, but rather that the moc own `#include` misses it AND the `qobjectdefs.h` also miss some of it's own dependencies as well. Only adding a long chain of internal `#include` solves the problem unless QObject is included (because it has that chain of include)