test build with libmemcached under cmake

Change-Id: Ie6b1d0b56accaa126366e9bb09cd103c282cfd85
Reviewed-on: http://review.couchbase.org/30172
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>