PHP 5.4+ in Local is not compiled with the mysql extension. It’s only compiled with pdo_mysql and mysqli.
You may be able to compile the mysql extension as a shared extension for 5.4-5.6 by following the instructions here: How do I compile additional PHP extensions?
As I’m sure you know, the best solution is to switch to a non-deprecated function that way you’ll be able to use PHP 7 in the future 