The cookbook scripts assume they have GNU utilities

available this causes problems in macOS which has an
BSD userland. With these changes we will use the GNU
`find` and `stat` installed by the now modified boostrap
script on https://github.com/redox-os/redox/pull/995.

Details

- Using `find` from Homebrew/MacPorts `findutils` package on macOS.
- Using `stat` from Homebrew/MacPorts `coreutils` package on macOS.