C++: Add isBarrier to CgiXss.ql.

cpp/ql/src/Security/CWE/CWE-079/CgiXss.ql

@@ -34,6 +34,10 @@ class Configuration extends TaintTrackingConfiguration {
   override predicate isSink(Element tainted) {
     exists(PrintStdoutCall call | call.getAnArgument() = tainted)
   }
+
+  override predicate isBarrier(Expr e) {
+    super.isBarrier(e) or e.getUnspecifiedType() instanceof IntegralType
+  }
 }
 
 from QueryString query, Element printedArg, PathNode sourceNode, PathNode sinkNode