skip modules whose mandatory dependencies are missing

so that for example "-skip webkit" will also skip qtwebkit-examples.

Task-number: QTBUG-30307
Change-Id: I730830781ea5dabdccab88d19e82165f30dca8fe
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>

qt.pro

@@ -27,8 +27,12 @@ defineTest(addModule) {
         export($${mod}.makefile)
     }
 
-    for(d, 2): \
-        $${mod}.depends += $$moduleName($$d)
+    for(d, 2) {
+        dn = $$moduleName($$d)
+        !contains(SUBDIRS, $$dn): \
+            return(false)
+        $${mod}.depends += $$dn
+    }
     for(d, 3) {
         dn = $$moduleName($$d)
         contains(SUBDIRS, $$dn): \