Support -ios triple

Autoconf hasn’t had an update since 2014, and it doesn’t look like it will soon[1]
This updates config.{guess,sub}

It adds support for e.g. `-ios`, which allows to have targets like `aarch64-apple-ios`.

It basically does exactly what the config.guess script says:
> It is advised that you download the most up to date version of the config scripts from

The configure.ac script has been updated to relax `*-apple-darwin*` to `*-apple-*`.
Similarly the `.gitignore` and `autogen.sh` needed to be updated to respect the
newer `config.{sub,guess}`

—
[1]: http://lists.gnu.org/archive/html/autoconf/2016-07/msg00017.html
5 files changed