Directory `/usr/include/php/` should be created if it does not exist

This is just a nitpick, but: trying to run the setup script on a barebones Ubuntu, both with Jammy and Focal, there is an error during the setup:

`ln: failed to create symbolic link '/usr/include/php/20XXYYZZ': No such file or directory`

I think it would be enough to create the dir '/usr/include/php' to fix that