Undefined behavior in QV4::ExecutionEngine::newArrayObject lead to crashes

Upcoming gcc-6 has much more aggressive dead-store elimination.
See: http://gcc.gnu.org/gcc-6/porting_to.html (-flifetime-dse section).

Due to undefined behavior in QV4::ExecutionEngine::newArrayObject(int)
this will lead to segfaults, e.g.:

Thread 1 "kdevelop" received signal SIGSEGV, Segmentation fault.
0x00007ffff4aac61a in QV4::ExecutionEngine::newArrayObject(int) () from /usr/lib/libQt5Qml.so.5
(gdb) bt
#0 0x00007ffff4aac61a in QV4::ExecutionEngine::newArrayObject(int) () from /usr/lib/libQt5Qml.so.5
#1 0x00007ffff4beadeb in QQmlObjectCreator::create(int, QObject*, QQmlInstantiationInterrupt*) () from /usr/lib/libQt5Qml.so.5
#2 0x00007ffff4bea830 in QQmlObjectCreator::createInstance(int, QObject*, bool) () from /usr/lib/libQt5Qml.so.5
#3 0x00007ffff4beac11 in QQmlObjectCreator::create(int, QObject*, QQmlInstantiationInterrupt*) () from /usr/lib/libQt5Qml.so.5
#4 0x00007ffff4bea830 in QQmlObjectCreator::createInstance(int, QObject*, bool) () from /usr/lib/libQt5Qml.so.5
#5 0x00007ffff4bec495 in QQmlObjectCreator::setPropertyBinding(QQmlPropertyData const*, QV4::CompiledData::Binding const*) () from /usr/lib/libQt5Qml.so.5
#6 0x00007ffff4bec68e in QQmlObjectCreator::setupBindings(QBitArray const&) () from /usr/lib/libQt5Qml.so.5
#7 0x00007ffff4be942f in QQmlObjectCreator::populateInstance(int, QObject*, QObject*, QQmlPropertyData const*, QBitArray const&) () from /usr/lib/libQt5Qml.so.5
#8 0x00007ffff4bea3da in QQmlObjectCreator::createInstance(int, QObject*, bool) () from /usr/lib/libQt5Qml.so.5
#9 0x00007ffff4beac11 in QQmlObjectCreator::create(int, QObject*, QQmlInstantiationInterrupt*) () from /usr/lib/libQt5Qml.so.5
#10 0x00007ffff4b71a47 in QQmlIncubatorPrivate::incubate(QQmlInstantiationInterrupt&) () from /usr/lib/libQt5Qml.so.5
#11 0x00007ffff4b720d6 in QQmlEnginePrivate::incubate(QQmlIncubator&, QQmlContextData*) () from /usr/lib/libQt5Qml.so.5
#12 0x00007ffff4b6d6f1 in QQmlComponent::create(QQmlIncubator&, QQmlContext*, QQmlContext*) () from /usr/lib/libQt5Qml.so.5
#13 0x00007ffff7a31dba in QQuickLoaderPrivate::_q_sourceLoaded() () from /usr/lib/libQt5Quick.so.5
#14 0x00007ffff7a32a10 in QQuickLoader::componentComplete() () from /usr/lib/libQt5Quick.so.5
#15 0x00007ffff4be6f28 in QQmlObjectCreator::finalize(QQmlInstantiationInterrupt&) () from /usr/lib/libQt5Qml.so.5
#16 0x00007ffff4b716c2 in QQmlIncubatorPrivate::incubate(QQmlInstantiationInterrupt&) () from /usr/lib/libQt5Qml.so.5
#17 0x00007ffff4b720d6 in QQmlEnginePrivate::incubate(QQmlIncubator&, QQmlContextData*) () from /usr/lib/libQt5Qml.so.5
#18 0x00007ffff4b6d6f1 in QQmlComponent::create(QQmlIncubator&, QQmlContext*, QQmlContext*) () from /usr/lib/libQt5Qml.so.5
#19 0x00007ffff7a31dba in QQuickLoaderPrivate::_q_sourceLoaded() () from /usr/lib/libQt5Quick.so.5
#20 0x00007ffff7a33979 in QQuickLoader::qt_static_metacall(QObject*, QMetaObject::Call, int, void**) () from /usr/lib/libQt5Quick.so.5
#21 0x00007ffff685c854 in QMetaObject::activate(QObject*, int, int, void**) () from /usr/lib/libQt5Core.so.5
#22 0x00007ffff4c3f96e in QQmlComponent::statusChanged(QQmlComponent::Status) () from /usr/lib/libQt5Qml.so.5
#23 0x00007ffff4b6c720 in QQmlComponentPrivate::typeDataReady(QQmlTypeData*) () from /usr/lib/libQt5Qml.so.5
#24 0x00007ffff4b8656d in QQmlTypeData::completed() () from /usr/lib/libQt5Qml.so.5
#25 0x00007ffff4b86f5c in QQmlTypeLoaderThread::callCompletedMain(QQmlDataBlob*) () from /usr/lib/libQt5Qml.so.5
#26 0x00007ffff4bf2051 in QQmlThreadPrivate::mainEvent() () from /usr/lib/libQt5Qml.so.5
#27 0x00007ffff4bf288e in QQmlThreadPrivate::MainObject::event(QEvent*) () from /usr/lib/libQt5Qml.so.5
#28 0x00007ffff714c09f in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#29 0x00007ffff71531d4 in QApplication::notify(QObject*, QEvent*) () from /usr/lib/libQt5Widgets.so.5
#30 0x00007ffff6830d00 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /usr/lib/libQt5Core.so.5
#31 0x00007ffff68334a5 in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) () from /usr/lib/libQt5Core.so.5
#32 0x00007ffff6884c73 in postEventSourceDispatch(_GSource*, int (void*), void*) () from /usr/lib/libQt5Core.so.5
#33 0x00007ffff286720e in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#34 0x00007ffff2867478 in g_main_context_iterate.isra () from /usr/lib/libglib-2.0.so.0
#35 0x00007ffff286752c in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#36 0x00007ffff688509f in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#37 0x00007ffff682f16a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /usr/lib/libQt5Core.so.5
#38 0x00007ffff683764d in QCoreApplication::exec() () from /usr/lib/libQt5Core.so.5
#39 0x000000000040cb40 in main ()

-flifetime-dse=1 "fixes" the issue, but of course it would be best to get rid of the UB.