Mark cleanup function as unused if compiled with QT_QML_NO_DEBUGGER

The static cleanup function in qqmldebugserver.cpp is only used if the
debug server is actually created. If not we can mark it as unused to
avoid compile warnings. Enclosing it in #ifdef would be uglier.

Task-number: QTBUG-42394
Change-Id: Ieb7fa38ecb346e80ce815ced85eb3a168bad9d99
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>

src/qml/debugger/qqmldebugserver.cpp

@@ -419,6 +419,7 @@ QQmlDebugServer::QQmlDebugServer()
         }
     }
 #else
+    Q_UNUSED(&cleanup)
     if (!appD->qmljsDebugArgumentsString().isEmpty()) {
         qWarning() << QString(QLatin1String(
                      "QML Debugger: Ignoring \"-qmljsdebugger=%1\". "