Compiling with QT_NO_WARNING_OUTPUT fails

g++ -c -pipe -march=i686 -mtune=generic -O2 -pipe -fstack-protector --param=ssp-buffer-size=4 -Wall -W -D_REENTRANT -DQT_NO_WARNING_OUTPUT -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/share/qt4/mkspecs/linux-g++ -I. -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtGui -I/usr/include/qt4 -I. -I. -o warntest.o warntest.cpp
In file included from /usr/include/qt4/QtCore/qnamespace.h:45:0,
from /usr/include/qt4/QtCore/qobjectdefs.h:45,
from /usr/include/qt4/QtCore/qobject.h:47,
from /usr/include/qt4/QtCore/qcoreapplication.h:45,
from /usr/include/qt4/QtCore/QCoreApplication:1,
from warntest.cpp:1:
/usr/include/qt4/QtCore/qglobal.h:1798:26: error: new declaration ‘QNoDebug qWarning()’
inline QNoDebug qWarning();
^
/usr/include/qt4/QtCore/qglobal.h:1791:29: error: ambiguates old declaration ‘QDebug qWarning()’
Q_CORE_EXPORT_INLINE QDebug qWarning();
^
make: *** [warntest.o] Error 1

This error doesn't occur with Qt 5.1.1.