sudo: fix -fstack-protector detection

Backport a patch series from upstream to fix the configure check for
-fstack-protector.

Fixes:
  http://autobuild.buildroot.net/results/bdd3e5352aa283b96717202a794f9762d15cc736/



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>