GNU autoconf-2.70 released

Thanks God we will "now" be able to rely on --runstatedir being there.

The option was added shortly _after_ autoconf 2.69 was released, 8 years ago. So it didn't actually exist in the wild... except by the vast amount of configure scripts that had been created in a Debian-based system, which added the patch to its package ages ago (https://sources.debian.org/patches/autoconf/2.69-10/add-r...). So you had people running autoreconf in non-Debian-based systems which had the option disappearing for them, with no idea why.