Ok , the good news is I now have a FreeBSD image which has Free Pascal on it . And the compiled cgi app worked fine on my web server.

To asnwer my own question, I downloaded the freebsd units and placed those in my free pascal units directory under i386-freebad. then you can compile using fpc <project> -Tfreebsd.

It can't actually produce the exe as the link stage fails but it does compile all the units, so you know if you unit will compile user freebsd as well as win32, I assume you can do the same for linux aswell.

Of course this doesn't mean you application will run under freebsd without testing but it goes along way to knowing if your code is portable