Use MARIADB_BASE_VERSION instead of LIBMARIADB to detect Maria DB [v9.16]
It was discovered that MariaDB 10 didn't define LIBMARIADB leading to compilation errors of MySQL DLZ modules on Debian stretch.
Use MARIADB_BASE_VERSION instead which is defined in all tested MariaDB versions.
(cherry picked from commit 5835aae6)
Closes #2813 (closed)
Edited by Ondřej Surý