Compiling an app made for linux

[Josh Paetzel]

I'm trying to compile a browser called flock from source.  My hope is 
to create a FBSD port for it.  The compile bombs out with the 
following error:

updater.o(.text+0x1373):/usr/home/jpaetzel/flock/mozilla/toolkit/mozapps/update/src/updater/updater.cpp:220: 
undefined reference to `pthread_join'
gmake[6]: *** [updater] Error 1

I have linux compat enabled.

What library do I have to feed to it so that it can use this function?

-- 
Thanks,

Josh Paetzel