MB-9469: include cstring to get std::memcpy

Change-Id: I88d0cc8ce3ddcd1ce245a0e095d5d1043a3c08a3
Reviewed-on: http://review.couchbase.org/30060
Tested-by: Volker Mische <volker.mische@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>