curl_share_cleanup(3) on macOS

The text e5d6eb4e2763, 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.

Clean up a shared object

curl_share_cleanup(3) on macOS now