qtscript: Check for QtGui before building the examples

qsdbg and marshal examples need QtGui module. If QtGui is not installed
they fail to compile.

Change-Id: I1af6a8b39a0848c8208fe94a26ee57409dfd9b41
Reviewed-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@digia.com>

examples/script/script.pro

 TEMPLATE = subdirs
-SUBDIRS = \
-    customclass \
-    qsdbg
+SUBDIRS = customclass
+
+qtHaveModule(gui): SUBDIRS += qsdbg
 
 qtHaveModule(widgets) {
     SUBDIRS += \
@@ -22,8 +22,7 @@ qtHaveModule(widgets) {
 }
 
 !wince {
-    SUBDIRS += \
-        marshal
+    qtHaveModule(gui): SUBDIRS += marshal
 }
 
 maemo5: CONFIG += qt_example