Skip xml test if no XML support is compiled.

modified:
  mysql-test/suite/connect/t/xml.test

mysql-test/suite/connect/t/xml.test

 --disable_query_log
---error 0
+--error 0,ER_UNKNOWN_ERROR
 CREATE TABLE t1 (a VARCHAR(10))
 ENGINE=CONNECT TABLE_TYPE=XML OPTION_LIST='xmlsup=libxml2';
 if (!`SELECT count(*) FROM INFORMATION_SCHEMA.TABLES