Incompatible for skip locked statements.

[cncal]

Bug Report

1. What did you do?

mysql> CREATE TABLE t (i INT, PRIMARY KEY (i)) ENGINE = InnoDB;
mysql> INSERT INTO t (i) VALUES(1),(2),(3);
mysql> SELECT * FROM t FOR UPDATE SKIP LOCKED;

2. What did you expect to see?

+---+
| i |
+---+
| 1 |
+---+
| 2 |
+---+
| 3 |
+---+

3. What did you see instead?

Error Code: 1064. You have an error in your SQL syntax; check the manual that corresponds to your TiDB version for the right syntax to use line 1 column 31 near "SKIP LOCKED" 

4. What version of TiDB SQL Parser are you using?

   v0.0.0-20200623082809-b74301ac298b

[ghost]

The TiDB issue for this is https://github.com/pingcap/tidb/issues/18207