FreeBSD cargo is distributed for an unsupported FreeBSD version (10.3).
FreeBSD 10.x is now unsupported, while cargo is being distributed for this version.
This is also reported here:
I am trying to build a new package based on the more recent FreeBSD 12.0 but I am a complete rookie, can someone address me on how to do it?
cargo package? Shall I specify --target? Please help.