curl_strequal(3) on macOS

The text 14dd2f5fad48, 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.

case insensitive string comparisons

curl_strequal(3) on macOS now