Some ports may have more than one `config.sub` that is in use (vendored
dependencies, etc.). Instead of fiddling about with space-delimited
strings, let's just make that setting into an array right away.
`mc` runs `autoconf` on the fly, which unpacks a `config.sub` from its
own files. This means that support for `serenity` (and the fact whether
the patch successfully applies) depends on the version of `autoconf`
that is installed on the host.
Instead, just always replace it with a fresh version straight from the
GNU server.
