Add s390x to configure file.
Add s390x to configure file.

For #6242.

JackieXie168/rethinkdb,JackieXie168/rethinkdb,grandquista/rethinkdb,JackieXie168/rethinkdb,jmptrader/rethinkdb,robertjpayne/rethinkdb,robertjpayne/rethinkdb,grandquista/rethinkdb,grandquista/rethinkdb,grandquista/rethinkdb,JackieXie168/rethinkdb,robertjpayne/rethinkdb,robertjpayne/rethinkdb,grandquista/rethinkdb,jmptrader/rethinkdb,grandquista/rethinkdb,grandquista/rethinkdb,robertjpayne/rethinkdb,JackieXie168/rethinkdb,grandquista/rethinkdb,JackieXie168/rethinkdb,JackieXie168/rethinkdb,jmptrader/rethinkdb,jmptrader/rethinkdb,robertjpayne/rethinkdb,jmptrader/rethinkdb,jmptrader/rethinkdb,jmptrader/rethinkdb,JackieXie168/rethinkdb,robertjpayne/rethinkdb,robertjpayne/rethinkdb,JackieXie168/rethinkdb,jmptrader/rethinkdb,robertjpayne/rethinkdb,grandquista/rethinkdb