mariadb 5.5.36 with innodb plugin
The method of using 'innodb_plugin' instead of default InnoDB is a MySQL 5.1 feature. The InnoDB plugin of 5.1 is the default of MySQL 5.5, and thus, in MySQL 5.5 we see this information for the 'ignore_builtin_innodb':


  In MySQL 5.1, this option caused the server to behave as if the built-in InnoDB were not present, which enabled InnoDB Plugin to be used instead. In MySQL 5.5, InnoDB is the default storage engine and InnoDB Plugin is not used, so this option has no effect. As of MySQL 5.5.22, it is deprecated and its use results in a warning.


This would be true for MariaDB 5.5 as well.