curl_share_cleanup(3) on macOS

The text 42fd5cf4c2f1, as Mac OS X 10.6.8, Mac OS X 10.6.7, Mac OS X 10.6.6, Mac OS X 10.6.5, Mac OS X 10.6.4, Mac OS X 10.6.3 shipped it.

Clean up a shared object

curl_share_cleanup(3) on macOS now