curl_share_init(3) on macOS

The text 28d27998b61e, as Mac OS X 10.7.5, Mac OS X 10.7.4, Mac OS X 10.7.3, Mac OS X 10.7.2, Mac OS X 10.7.1, Mac OS X 10.7 shipped it.

Create a shared object

curl_share_init(3) on macOS now