lua: Increase reserved stack space for FreeBSD in debug config

lua: Increase reserved stack space for FreeBSD in debug config

FreeBSD uses more stack space in debug configurations and can overflow
the stack while formatting the error message when the call depth limit
of 20 frames is reached.  This is readily reproduced by running the
gsub recursion test with increased kstack size.  I hit the panic with
16 pages per kstack, and noticed it go away when bumped to 17.

Reserve an additional 64 bytes on the stack when building for FreeBSD.
This is enough to avoid the panic with a deep stack while not wasting
too much space when the default stack size is used.

Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes #10634