mysql_connect() has been finally removed from PHP7 (it was deprecated for some time), and now you have to use mysqli_connect();  The same goes for any other mysql_ commmand. (I simply did a find/replace for “mysql_” and changed it to “mysqli_” in my php code.
Also, if you’re running your own server, you probably need to install the “php-mysql” after upgrading to PHP7 — it doesn’t seem to be installed along by default anymore.