I've got a possible fix for this at https://trac.torproject.org/projects/tor/ticket/31687 , but it needs testing; please let me know if it works for you.
As near as I can tell, this code has been unchanged for a while, so I'm surprised if these warnings are new in 0.4.1. Is it possible that a new compiler version or new headers in FreeBSD is what has made them start appearing? (In other words, do you see these warnings if you go back and build 0.4.0 or 0.3.5?)
peace,