* data/c.m4 (b4_error_verbose_if): New.

* data/c.m4 (b4_error_verbose_if): New.
* data/lalr1.cc: Use it.
(YYERROR_VERBOSE_IF): Remove.
(yyn_, yylen_, yystate_, yynerrs_, yyerrstatus_): Remove as
parser members, replaced by...
(yyn, yylen, yystate, yynerss, yyerrstatus): these parser::parse
local variables.
(yysyntax_error_): Takes the state number as argument.
(yyreduce_print_): Use the argument yyrule, not the former
attribute yyn_.