core-file should become a real server variable

The actual setting of core-file can't be detected at run time (unless applying some gdb magic maybe). So it is not possible to tell whether a mysqld process may write a core dump or not, or to identify servers where core-file may be missing from the configuration.

This was the same in MySQL until MySQL 5.5.x, but in MySQL 5.6 and above the value of core-file is exposed in SHOW VARIABLES output.

MySQL 5.6:

mysql> show variables like 'core_file';

+---------------+-------+

| Variable_name | Value |

+---------------+-------+

| core_file     | ON    |

+---------------+-------+

MariaDB 10.3:

mysql> show variables like 'core_file';

Empty set (0.00 sec)