QLayout base class destructor not virtual

The destructor definition in QLayout in qtbase src/widgets/kernel/qlayout.h does not have a virtual specifier. It seems most all compilers in use building Qt and Qt applications assume this will be virtual and mark it so, however this is non-standards-conforming behavior.

According to the standard, it should be marked virtual.
This is pretty clear (though this isn't a direct copy of the standard - that is behind a paywall):
https://en.cppreference.com/w/cpp/language/destructor#Virtual_destructors
 

class Q_WIDGETS_EXPORT QLayout : public QObject, public QLayoutItem
{
    Q_OBJECT
[...]
public:
[...]
    QLayout(QWidget *parent);
    QLayout();
    ~QLayout();