dlopen() and friends are included in libc on FreeBSD.
o Use './controller/block_list.sh' (with explicit "./") because '.' isn't on
  the $PATH by default on FreeBSD.
o Disable joystick block for now on FreeBSD due to lack of use case and
  inspiration to port :)
o Use a compatibility hack so we can use 'sed' with the same command line
on Linux and FreeBSD.
o Use '/usr/local/bin/flex' explicitly on FreeBSD since FreeBSD can have
  both BSD flex and GNU flex installed as 'flex', where the former has
  precendence on the normal $PATH.