CURLOPT_IPRESOLVE(3) on macOS

The text 97aadfdb0024, as macOS 10.12.5, macOS 10.12.4, macOS 10.12.3, macOS 10.12.2, macOS 10.12.1, macOS 10.12 shipped it.

specify which IP protocol version to use

CURLOPT_IPRESOLVE(3) on macOS now