Fake exporting of the QDBusUtil namespace

It's a namespace containing only private things, but some of those get
used in some QtDBus tools. By adding a macro that expands to nothing,
findclasslist.pl will notice the namespace and add it to the ELF version
script.

Task-number: QTBUG-55897
Change-Id: I371f5b01e24a4d56b304fffd1472748cde56f0c3
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

src/dbus/qdbusutil_p.h

@@ -64,7 +64,8 @@
 
 QT_BEGIN_NAMESPACE
 
-namespace QDBusUtil
+#define Q_DBUS_NO_EXPORT        // force findclasslist.pl looking into this namespace
+namespace Q_DBUS_NO_EXPORT QDBusUtil
 {
     Q_DBUS_EXPORT bool isValidInterfaceName(const QString &ifaceName);