Compiled PHP 7 missing mysql extension in WordPress

Question

I have built PHP 7 with a configuration that worked for a previous version of PHP. Now my WordPress websites get the message:

Your PHP installation a

Answer 1

Check if the Wordpress still using the Mysql extension that was removed in PHP7.

http://php.net/manual/en/migration70.removed-exts-sapis.php

The Mysqli and PDO extensions were kept. This is the reason your other websites are working.