make sure Xlib is in our dependencies

Task-number: QTCREATORBUG-11107
Change-Id: I5d0bc2cb34a1c02e2c310df4bd40fa9df198292d
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/libs/utils/utils.pro

@@ -10,6 +10,7 @@ lessThan(QT_MAJOR_VERSION, 5) {
 } else:linux-* {
     !isEmpty(QT.x11extras.name) {
         QT += x11extras
+        CONFIG += x11
         DEFINES += QTC_USE_QX11INFO
     } else {
         warning("x11extras module not found, raising the main window might not work. " \