Fix compile on Yosemite

Change-Id: I7576345b43f8915f047b9bc1a690670dc241427e
Reviewed-on: http://review.couchbase.org/42306
Reviewed-by: Jim Walker <jim@couchbase.com>
Reviewed-by: Daniel Owen <owend@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>