The source doesn't build because of a typo, which makes me tell this code was only tested in theory :) See in os.c at line 122, there is FALSE1 and it has to be FALSE. Now this being fixed, the code builds, but the tooltip that shows the cpu usage in percent is wrong, it displays a value around one million percent. I will see to attach a patch later.
As I don't have a FreeBSD system at hand, I indeed didn't test it. But you did, so everything is fine, right? ;) I just committed the fix for the typo you complained about here, so I'll close this bug. I opened Bug 6530 for the tooltip problem.