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

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.