ORACLE MySQL 8.0 has dropped the my_bool type, so we need to reinstate
it back when compiling with that version or higher.  MariaDB is still
keeping the my_bool type.  The numbering between the two (MariaDB 5.x
jumped to MariaDB 10.x) doesn't make the life of the developer easy.

(cherry picked from commit c6d5d5c8)