Linux v4.11: signal stuff moved to sched/signal.h

Linux v4.11: signal stuff moved to sched/signal.h

In Linux commit c3edc4010e9d102eb7b8f17d15c2ebc425fed63c, signal_struct
and other signal handling declarations were moved from sched.h to
sched/signal.h.

This breaks existing OpenAFS autoconf tests for recalc_sigpending() and
task_struct.signal->rlim, so that the OpenAFS kernel module can no
longer build.

Modify OpenAFS autoconfig tests to cope.

Reviewed-on: https://gerrit.openafs.org/12573
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Joe Gorse <jhgorse@gmail.com>
Tested-by: Joe Gorse <jhgorse@gmail.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
(cherry picked from commit ad001550949b612ff6b4899fa8da50ee58f87533)

Change-Id: I491208d77e45d45cc0089b8033892a6408da431c
Reviewed-on: https://gerrit.openafs.org/12589
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>