mysql57 now fails to build on FreeBSD 9 with libressl

[mokhi]

Hi.
Your change now makes building on all 9.x broken.

Actually the problem is mysql57's needed minimum version of openssl is
newer than what we have as openssl-base on 9.x
So to support building and running it on all freebsd versions we need
two branches of rules in Makefile.
For 9.x we should install openssl from ports.
For newer (>= 10) nothing is needed to be changed and openssl-base in
enough (and port can be chosen by user from configs).

The problem goes more complex to deal with when it comes to support
libressl too.

I understand why you say it's stupid to change defaults in the
Makefile, but I just added `WITH_OPENSSL_PORT=yes` to Makefile and
poudriere suggested me to change it to `DEFAULT_VERSIONS+=ssl=openssl`

BTW, if you think there's no better way to fix building it on 9.x, we
can mark port as ignore/broken on 9.x (and notify users that they can
add such statement to their make.conf) till we find a better way.

Best Regards, Mokhi.