OpenSceneGraph has overridden virtuals defined in its headers

Use a pragma around our use of that header to silence the warning. OSG
3.01 has these warnings, 3.2 has fixed them, but 3.2 doesn’t isn’t the
widely used release yet. So at some point when we upgrade to 3.2 this
will no longer be needed.

src/ui/map3D/Q3DWidget.h

@@ -39,8 +39,20 @@ This file is part of the QGROUNDCONTROL project
 #include <osg/PositionAttitudeTransform>
 #include <osgGA/TrackballManipulator>
 #include <osgText/Font>
+
+// OpenSceneGraph has overloaded virtuals defined, since third party code we silence the warnings when the
+// headers are used.
+#ifndef Q_OS_WIN
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Woverloaded-virtual"
+#endif
+
 #include <osgViewer/Viewer>
 
+#ifndef Q_OS_WIN
+#pragma GCC diagnostic pop
+#endif
+
 #include "CameraParams.h"
 #include "GCManipulator.h"
 #include "SystemGroupNode.h"