I’m PHP7 and PDO all the way for anything I am developing, but it’s rather hard to update an old code base if I can’t run it in the first place! Thanks for linking to the instructions for adding in the extension - unfortunately I couldn’t get that to work. I got as far as the configure step not generating anything that looks like an error but then make gave lots of errors.
For this project, I’ve reverted to MAMP, at least until I get it PHP7 compatible, but thanks for the help.