Ensure the system libraries are linked against when -no-opengl is used

Task-number: QTBUG-40406
Change-Id: I1e166a5003f524cdeb4a53d78a382a6b11719b6a
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/plugins/directshow/directshow.pro

 TARGET = dsengine
-
+win32:!qtHaveModule(opengl) {
+    LIBS_PRIVATE += -lgdi32 -luser32
+}
 PLUGIN_TYPE=mediaservice
 PLUGIN_CLASS_NAME = DSServicePlugin
 load(qt_plugin)