Set the `virtual' attribute.

src/shared/cplusplus/CheckDeclaration.cpp

@@ -190,6 +190,7 @@ bool CheckDeclaration::visit(SimpleDeclarationAST *ast)
             fun->setScope(_scope);
             fun->setName(name);
             fun->setMethodKey(semantic()->currentMethodKey());
+            fun->setVirtual(qualTy.isVirtual());
             if (isQ_SIGNAL)
                 fun->setMethodKey(Function::SignalMethod);
             else if (isQ_SLOT)