vos: Mark longjmp-used variables as 'volatile'

vos: Mark longjmp-used variables as 'volatile'

vsprocs tries to do error recovery by calling longjmp from a signal
handler. Although this is quite error-prone since we call a ton of
non-async-signal-safe functions, make it a bit more likely to work by
marking variables that are used after the longjmp as volatile. This
reduces how often (depending on the platform) these values will be
completely worthless after a longjmp since they were cached in a
register or similar.

FIXES 125535

Reviewed-on: http://gerrit.openafs.org/1557
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit fe3ff8e91237f35fed33d6d417830e0fe44c6479)

Change-Id: I6d63f516a0864c643f5fea2a711a8adea9fdcc6d
Reviewed-on: http://gerrit.openafs.org/3573
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit f6a272c69683cbb9fcd7e23ff693dd6c57c0e1ac)