Use RTEMS_SYSINIT_ORDER_LAST_BUT_5 instead of RTEMS_SYSINIT_ORDER_LAST
to allow applications and support functions to place system
initialization handlers behind the standard handlers.
Update #3838.
Relicense contributions from Chris Johns, Christian Mauderer,
embedded brains GmbH, Joel Sherrill, OAR, Pavel Pisa, Ralf Kirchner, and
Sebastian Huber.
Update #3053.