Fix databases/mariadb* hostname verification when building against LibreSSL
LibreSSL imported X509_check_host from BoringSSL. Unlike OpenSSL,
it doesn't calculate the length of the hostname passed in case
chklen/namelen == 0. This means that the check in MariaDB always
fails if built against LibreSSL. This forces adminstrators to disable
hostname verification, which weakens security (hence the MFH request below).
Note that the fix has no negative implications if built against OpenSSL,
as its implementation calls strlen(hostname) in case namelen == 0.
See also https://github.com/MariaDB/server/pull/562
Approved by: ssl blanket