Enable build of platform layer

Change-Id: I0b2e1a7c530da56c769b6060cecd0aa0900c78ba
Reviewed-on: http://review.couchbase.org/28439
Tested-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: Sriram Melkote <siri.couchbase@gmail.com>