(%union synch line): Put a dummy member in

the union, because empty unions aren't allowed in C.
Caught by GCC 3.4.0.

tests/synclines.at

@@ -1,5 +1,5 @@
 # Executing Actions.                               -*- Autotest -*-
-# Copyright (C) 2002 Free Software Foundation, Inc.
+# Copyright (C) 2002, 2004 Free Software Foundation, Inc.
 
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -100,6 +100,7 @@ exp: '0';
 AT_TEST_SYNCLINE([%union synch line],
 [[%union {
 #error "2"
+  char dummy;
 }
 %{
 void yyerror (const char *s);