curl_multi_setopt(3) on macOS

The text 816123d27ce0, 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.

set options for a curl multi handle

curl_multi_setopt(3) on macOS now