In addition to the shim and compat libs recommended, I've had decent luck with the converter tool (https://github.com/philip/MySQLConverterTool https://github.c

In addition to the shim and compat libs recommended, I've had decent luck with the converter tool (https://github.com/philip/MySQLConverterTool https://github.com/philip/MySQLConverterTool). It goes a bit out of its way to be compatible so one function call can get expanded into a global var + function call. phpcs + PHPCompatibility ruleset is pretty good about finding issues as well.