Fix yyerror / yylex test glitches noted by [email protected].

* tests/cxx-type.at (_AT_TEST_GLR_CXXTYPES): Have yyerror return
void, not int.
* tests/glr-regression.at (Badly Collapsed GLR States):
Likewise.
(Improper handling of embedded actions and dollar(-N) in GLR parsers):
yylex should return 0 at EOF rather than aborting.

tests/cxx-type.at

@@ -56,7 +56,7 @@ $1
 # define ERROR_PARAMETERS char const *s
 #endif
   int yylex (LEX_PARAMETERS);
-  int yyerror (ERROR_PARAMETERS);
+  void yyerror (ERROR_PARAMETERS);
 %}
 
 %token TYPENAME ID
@@ -191,7 +191,7 @@ yylex (LEX_PARAMETERS)
     }
 }
 
-int
+void
 yyerror (ERROR_PARAMETERS)
 {
 #if YYPURE && YYLSP_NEEDED