vm_eval.c: all value type cases

* vm_eval.c (rb_type_str): ensure all value types are covered.
  missed types would be warned by -Wswitch option of gcc.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60395 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

vm_eval.c

@@ -470,9 +470,10 @@ rb_type_str(enum ruby_value_type type)
       type_case(T_NODE)
       type_case(T_ICLASS)
       type_case(T_ZOMBIE)
-      default: return NULL;
+      case T_MASK: break;
     }
 #undef type_case
+    return NULL;
 }
 
 NORETURN(static void uncallable_object(VALUE recv, ID mid));