libedit changed its interface a while back. mariadb currently does not
recognize this interface and instead uses a static old readline version.
It does not link in the system readline due to licence incompatibility.

This commit adds a patch that enables mariadb to detect and use the
system libedit. The patch was sent upstream already ([1]).

[1] https://github.com/MariaDB/server/pull/1001

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>