Came here to say the same. I've used them long-term on legacy codebases and they work great for allowing new development to move onto modern PHP.
While I'm using https://github.com/dshafik/php7-mysql-shim, another to look at is https://github.com/mattbit/mysql-compat
https://github.com/dshafik/php7-mysql-shim
It won't be 100% perfect and it's definitely not something I'd want to use long term, but it can help with the initial migration to PHP 7.