curl_share_setopt(3) on macOS

The text afb6dbff4481, 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.

Set options for a shared object

curl_share_setopt(3) on macOS now