Change paths of jail and ports to something shorter.  I hit MNAMELEN (88 characters) a few times
when doing nullfs mounts.
Create a valid /wrkdirs directory in the jail we will use to build ports.
Add this to /etc/make.conf in the jail.

This logic is taken from jail.sh in poudriere.  poudriere needs
this stuff set up properly before it can build ports.
Set USE_TMPFS so that tmpfs will only be used for the wrkdir of each port.
Add debug.