Suppress a warning from source generated by Lemon

    ecmascript.c: In function 'yy_destructor':
    ecmascript.c:73:45: warning: unused variable 'efsi' [-Wunused-variable]
     #define grn_expr_parserARG_FETCH  efs_info *efsi  = yypParser->efsi
                                                 ^
    ecmascript.c:861:3: note: in expansion of macro 'grn_expr_parserARG_FETCH'
       grn_expr_parserARG_FETCH;
       ^