cmake: install "libuv_compat.h" header

This breaks compilation otherwise for couchnode with a dynamic
libcouchbase

Change-Id: Ibdbd78e864bef4ef024e9745477b074a68113a73
Reviewed-on: http://review.couchbase.org/41655
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>