Detect HAVE_LARGE_STACKS at compile time (#12584)

Move HAVE_LARGE_STACKS definitions to header and set when appropriate.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Allan Jude <allan@klarasystems.com>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Kevin Bowling <kbowling@FreeBSD.org>
Closes #12350