configure: check for poll()

configure: check for poll()

if we have code which uses HAVE_POLL, check for poll().

Reviewed-on: http://gerrit.openafs.org/8357
Reviewed-by: Chaskiel Grundman <cg2v@andrew.cmu.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
(cherry picked from commit 7fe30bd28e62ad0ed717c24e8eccf5e563b9cd68)

Change-Id: I99a25d20d0d98e516d72f885feef2a4d15ca01fb
Reviewed-on: http://gerrit.openafs.org/8367
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>