In FreeBSD base system revision 315662 hid the struct inpcb and struct tcpcb from userland.
struct xinpcb and struct xtcpcb should be used in their place, which contain only userland parts. No kernel space references.
The version of psutil embedded in 0ad needs paatching to compile on recent FreeBSD versions.
Attached patch is base on the one in the psutil 1.2.1 port present in the FreeBSD ports tree which has the same problem.