cmake: Build libuv on Windows, if found

Change-Id: Ibb6bb0b393322a731dc0743cb1c7b2aff5f64a68
Reviewed-on: http://review.couchbase.org/41471
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>