Make zlib test portable

Change-Id: Iefb995bf398caed3820430e66b70c23bc10545b0
Reviewed-on: http://review.couchbase.org/31682
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>