Patch to enable SSP on RELENG_7/CURRENT by default

Hi list,

I already posted a couple of month ago for a patch to bring in
ProPolice/SSP into 6-STABLE and 7-CURRENT [1].  Understandably, it has
never been commited because this required to heavily patch GCC 3.4.6,
which is a contributed software.

Now that RELENG_7 and CURRENT have GCC 4.2.1, which provides SSP,
FreeBSD just lacks the "glue" bits to make the best of it.  Once
applied, FreeBSD will be compiled with SSP unless WITHOUT_SSP is set.

This patch is a kind of proof of concept.  For example, the FreeBSD
team might not want to enable SSP by default (any benchmark from other
users than me would be welcome).  The Makefile guy(s?) may also have
comments on how I've implemented it in the build infrastructure
(SSP_CFLAGS notably).  Also, the kernel bits I scrawled in
sys/kern/stack_protector.c should surely be improved.

Best regards,

[1] http://tataz.chchile.org/~tataz/FreeBSD/SSP/
-- 
Jeremie Le Hen
< jeremie at le-hen dot org >< ttz at chchile dot org >