Use %pure-parser instead of the deprecated %pure_parser.

Author: dr-m

sql/sql_yacc.yy

@@ -959,7 +959,7 @@ static bool sp_create_assignment_instr(THD *thd, bool no_lookahead)
 bool my_yyoverflow(short **a, YYSTYPE **b, ulong *yystacksize);
 %}
 
-%pure_parser                                    /* We have threads */
+%pure-parser                                    /* We have threads */
 %parse-param { THD *thd }
 %lex-param { THD *thd }
 /*