The wiki page seems to imply that GDLib comes with PHP. Unfortunately, the instructions to check if GDLib is still present are confusing to me. What is meant by "If you install a file including the code <?php phpinfo(); ?>
on your webserver and open the URL to the file in a browser, then information about the installed PHP version will appear."
I was able to find the following comment on
https://jason.pureconcepts.net/2016/09/update-apache-php-mysql-mac-os-x-sierra/
The comment is: "Mac OS X Sierra comes pre-installed with PHP version 5.6, however the latest version of PHP is 7.1. After you complete this post, you should upgrade PHP on Mac OS X."
I am not sure what to make of this.