lang/rust: Add support for LibreSSL 2.6.1 and 2.6.2
Patches come from upstream:
https://github.com/sfackler/rust-openssl
PR: 222359
Reported by: Charlie Li <ml+freebsd-bugs@vishwin.info>,
Piotr Kubaj <pkubaj@anongoth.pl>, w.schwarzenfeld@utanet.at, nhoyle@hoyletech.com