Include <sys/wait.h> for homebrew-acceptance.test.c

Needed for WIFSIGNALED et al

Change-Id: I3602d6c6b22dc5776ec19c8689d78cf2f7aacfae
Reviewed-on: http://review.couchbase.org/39948
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Dave Rigby <daver@couchbase.com>