xo-reader: + exprseq_xs.on_typedef() + simplie tl exprseq case

include/xo/reader/exprseq_xs.hpp

@@ -31,6 +31,10 @@ namespace xo {
 
             // ----- victory methods -----
 
+            virtual void on_typedescr(TypeDescr /*td*/,
+                                      exprstatestack * /*p_stack*/,
+                                      rp<Expression> * /*p_emit_expr*/) override;
+
         };
     } /*namespace scm*/
 } /*namespace xo*/