Let yyerror always receive the msg as last argument, so that

yyerror can be variadic.
* data/yacc.c (b4_yyerror_args): New.
Use it when calling yyerror.
* data/glr.c (b4_yyerror_args, b4_lyyerror_args): New.
Use it when calling yyerror.
* doc/bison.texinfo (Error Reporting): Adjust.
* tests/calc.at (_AT_DATA_CALC_Y): Adjust.
* tests/cxx-type.at (_AT_TEST_GLR_CALC): Adjust.

tests/calc.at

@@ -100,9 +100,9 @@ static int power (int base, int exponent);
 /* yyerror receives the location if:
    - %location & %pure & %glr
    - %location & %pure & %yacc & %parse-param. */
-static void yyerror (const char *s
-                     ]AT_YYERROR_ARG_LOC_IF([, YYLTYPE *yylloc])[
-                     ]AT_PARAM_IF([, value_t *result, int *count])[
+static void yyerror (]AT_YYERROR_ARG_LOC_IF([YYLTYPE *yylloc, ])[
+                     ]AT_PARAM_IF([value_t *result, int *count, ])[
+                     const char *s
                      );
 static int yylex (LEX_FORMALS);
 static int yygetc (LEX_FORMALS);
@@ -154,9 +154,10 @@ exp:
 FILE *yyin;
 
 static void
-yyerror (const char *s
-         ]AT_YYERROR_ARG_LOC_IF([, YYLTYPE *yylloc])[
-         ]AT_PARAM_IF([, value_t *result, int *count])[)
+yyerror (]AT_YYERROR_ARG_LOC_IF([YYLTYPE *yylloc, ])[
+         ]AT_PARAM_IF([value_t *result, int *count, ])[
+         const char *s
+         )
 {
 ]AT_PARAM_IF([(void) result; (void) count; ])[
 ]AT_YYERROR_SEES_LOC_IF([

tests/cxx-type.at

@@ -36,10 +36,11 @@ $1
 ]m4_bmatch([$2], [stmtMerge],
 [ static YYSTYPE stmtMerge (YYSTYPE x0, YYSTYPE x1);])[
   #define YYINITDEPTH 10
-  int yyerror (const char *s
+  int yyerror (
 #if YYPURE && YYLSP_NEEDED
-               , YYLTYPE *yylocation
+               YYLTYPE *yylocation,
 #endif
+               const char *s
               );
 
   #if YYPURE
@@ -157,10 +158,11 @@ yylex ()
 }
 
 int
-yyerror (const char *s
+yyerror (
 #if YYPURE && YYLSP_NEEDED
-        , YYLTYPE *yylocation
+         YYLTYPE *yylocation,
 #endif
+         const char *s
         )
 {
 #if YYPURE && YYLSP_NEEDED