MFC r318210,r318211:

Approved by: re (gjb)

r318210:

ssp_test:read:: query the value of MAXPATHLEN via getconf(1)

In the event the value of PATH_MAX was changed, the assumption that
MAXPATHLEN is 1024 (and hence the buffer length required to trigger
SSP to fail for read(2)) would be invalidated. Query getconf(1) for
the actual value of MAXPATHLEN via _XOPEN_PATH_MAX instead, and
increment the value by 1 to ensure that the SSP support tests the
stack smashing support properly.

r318211:

Fix up previous commit

• Apply the logic to the FreeBSD block
• Fix a typo with the getconf(1) call that I would have caught, were it not for the fact that I got the blocks wrong.
• Consolidate the hardcoded buffer sizes to the NetBSD block.

This would have been discovered had I run the test on a system where
PATH_MAX != 1024 (I don't have that at my disposal right at this moment).

MFC with: r318210