Move sigar and portsigar to cmake

Change-Id: I65908e1e83981a8aa2ecf00d6d109b348e5346c0
Reviewed-on: http://review.couchbase.org/30664
Tested-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: Michael Wiederhold <mike@couchbase.com>