MDEV-9106 Audit Plugin doesn't run with MySQL 5.7.     MariaDB 5.5 built in debug gets unhappy with mutexes.     Although everything is correct, some DBUG_ASSERT can happen.     So this patch keeps safe_mutex silent.
MDEV-9106 Audit Plugin doesn't run with MySQL 5.7.
    MariaDB 5.5 built in debug gets unhappy with mutexes.
    Although everything is correct, some DBUG_ASSERT can happen.
    So this patch keeps safe_mutex silent.

ollie314/server,natsys/mariadb_10.2,natsys/mariadb_10.2,ollie314/server,flynn1973/mariadb-aix,ollie314/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,ollie314/server,natsys/mariadb_10.2,flynn1973/mariadb-aix,ollie314/server,flynn1973/mariadb-aix,flynn1973/mariadb-aix,natsys/mariadb_10.2,natsys/mariadb_10.2,flynn1973/mariadb-aix,slanterns/server,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,ollie314/server,flynn1973/mariadb-aix,flynn1973/mariadb-aix,flynn1973/mariadb-aix,natsys/mariadb_10.2,ollie314/server,flynn1973/mariadb-aix,ollie314/server,ollie314/server,natsys/mariadb_10.2,ollie314/server,ollie314/server,flynn1973/mariadb-aix