add powerpc64 target
The bootstrap files were generated on 11.2 and are available here:
http://mikael.urankar.free.fr/FreeBSD/powerpc64/cargo-0.31.0-powerpc64-unknown-freebsd.tar.gz
http://mikael.urankar.free.fr/FreeBSD/powerpc64/rust-std-1.30.1-powerpc64-unknown-freebsd.tar.gz
http://mikael.urankar.free.fr/FreeBSD/powerpc64/rustc-1.30.1-powerpc64-unknown-freebsd.tar.gz
cargo is broken on 12.0, it's linked with openssl from a 11.2 system. I've asked the rust@ team how to statically link openssl, libgit, libssh2,libcurl but got no response.
I'm adding reviewers based on this list https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=232171