LibreSSL, DragonFly, and dports

It’s now possible to build dports using LibreSSL instead of OpenSSL.  Set SSL_DEFAULT in make.conf to the appropriate port name, and start building.  Use synth for fastest results, of course.

LibreSSL will eventually become the default library.  This is in addition to the previously-mentioned, already-completed in DragonFly 4.7, base system switch to LibreSSL.