Qt5: Fix checking for private headers

Change-Id: I66ea39bb4ced671f3ccd6f926fa43e629e2c1251
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

src/plugins/qnx/qnx.pro

@@ -161,11 +161,17 @@ FORMS += \
     blackberrydebugtokenrequestdialog.ui
 
 include(../../private_headers.pri)
-exists($${QT_PRIVATE_HEADERS}/QtGui/private/qzipreader_p.h) {
+
+greaterThan(QT_MAJOR_VERSION, 4) {
+    QT += gui-private
     DEFINES += QNX_ZIP_FILE_SUPPORT
 } else {
-    warning("The QNX plugin depends on private headers from QtGui module, to be fully functional.")
-    warning("To fix it, pass 'QT_PRIVATE_HEADERS=$QTDIR/include' to qmake, where $QTDIR is the source directory of qt.")
+    exists($${QT_PRIVATE_HEADERS}/QtGui/private/qzipreader_p.h) {
+        DEFINES += QNX_ZIP_FILE_SUPPORT
+    } else {
+        warning("The QNX plugin depends on private headers from QtGui module, to be fully functional.")
+        warning("To fix it, pass 'QT_PRIVATE_HEADERS=$QTDIR/include' to qmake, where $QTDIR is the source directory of qt.")
+    }
 }
 
 DEFINES += QT_NO_CAST_TO_ASCII QT_NO_CAST_FROM_ASCII