qdbuscpp2xml/qdbusxml2cpp: Avoid producing code that won't compile

// counter.h
#ifndef COUNTER_H
#define COUNTER_H

#include <QObject>

class Counter : public QObject
{
    Q_OBJECT
    Q_PROPERTY(int value READ value WRITE setValue NOTIFY valueChanged);

public:
    Counter(QObject* parent = nullptr);
    int value() const { return m_value; }

public slots:
    void setValue(int value);

signals:
    void valueChanged(int newValue);

private:
    int m_value = 0;
};
#endif

class CounterAdaptor: public QDBusAbstractAdaptor
{
    Q_OBJECT
    Q_CLASSINFO("D-Bus Interface", "local.Counter")
    // ...

public: // PROPERTIES
    Q_PROPERTY(int value READ value WRITE setValue)
    int value() const;
    void setValue(int value);

public Q_SLOTS: // METHODS
    void setValue(int value);
Q_SIGNALS: // SIGNALS
    void valueChanged(int newValue);
};