Remove `YYERROR_VERBOSE` which no longer supported since `bison 3.6`.
Instead we added `%define parse.error verbose`.
MODIFY
mrbgems/mruby-compiler/core/parse.y
mrbgems/mruby-compiler/core/parse.y
#ifdef PARSER_DEBUG
# define YYDEBUG 1
#endif
-#define YYERROR_VERBOSE 1
#define YYSTACK_USE_ALLOCA 1
#include <ctype.h>
@@ -1330,6 +1329,7 @@ heredoc_end(parser_state *p)
%}
+%define parse.error verbose
%define api.pure
%parse-param {parser_state *p}
%lex-param {parser_state *p}

Remove `YYERROR_VERBOSE` which no longer supported since `bison 3.6`.

Instead we added `%define parse.error verbose`.