`which` is not guaranteed to be installed on all machines. Since the
script is meant to be run on the user's host machine it is more portable
to use `type -p` here.
Closes: https://github.com/dockcross/dockcross/issues/880
All images built for a linux/amd64 host.
Addresses warning when running an Apple M1:
WARNING: The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested