make use of qtHaveModule()

Change-Id: Iff51a71f1d24a1372359efcea74d627ae4d471ee
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>
Reviewed-by: Tasuku Suzuki <stasuku@gmail.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

examples/xmlpatterns/xmlpatterns.pro

 TEMPLATE = subdirs
 SUBDIRS += xquery
-!contains(QT_CONFIG, no-widgets): SUBDIRS += filetree schema recipes
+qtHaveModule(widgets): SUBDIRS += filetree schema recipes
 
 EXAMPLE_FILES = \
     shared