dsynth - Optimize pty use
* Have the WORKER process allocate the pty once and use it in all
phases, instead of allocating and closing a new pty for each phase.
* Make N copies of /bin, /lib, /usr/bin, and /libexec into the base
directory and mount those in the chroots instead of the system
directory, essentially unsharing these directories. Each worker
gets an independent copy.
This should reduce contention and cache-line ping-ponging overhead
on /bin/sh, libc, make, etc, significantly.
* Create the template conditionally whether 'pkg' has been built or
not.
UnifiedSplitRaw