CURLOPT_SSLENGINE(3) on macOS

The text bd43e118fc9b, 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.

set SSL engine identifier

CURLOPT_SSLENGINE(3) on macOS now