Basically to get binaries that can run on free BSD
If you want to compile something that runs on free BSD, implies you have access to a Free BSD system. To which you can just compile them on that very same BSD system.
Because you are seeking to do this on a Red Hat system, "implies" you don't have rights to do it on that BSD system, which further leads me to assume you are trying to circumvent "policy" imposed upon you/public that limits you/public from running malicious software/code/binaries or similar on "the" Free BSD system/network you want to run these binaries on.
Because Free BSD is "free", and you can install it on your system that has Linux, leads me to believe you are looking for a shortcut in achieving your malicious "goal".