qlocationlabsglobal_p.h: Add missing "We mean it" comment

Fix:
WARNING: qtlocation/src/locationlabs/qlocationlabsglobal_p.h does not have the "We mean it." warning

Change-Id: Iae44606739fce82d113dfdd228a44e1911593598
Reviewed-by: Paolo Angelelli <paolo.angelelli@qt.io>

src/locationlabs/qlocationlabsglobal_p.h

@@ -36,6 +36,17 @@
 #ifndef QLOCATIONLABSGLOBAL_P_H
 #define QLOCATIONLABSGLOBAL_P_H
 
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API. It exists purely as an
+// implementation detail. This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
 #include <QtCore/qglobal.h>
 
 QT_BEGIN_NAMESPACE