Add an armel build like the i386ancient build.

The current arm autobuilder doesn't have enough free space for the chroot
this would need. I need to upgrade its microsd card first, adding
approximately 5 gb. (A 16 gb card would suffice.)

Now, it would be possible to switch it to only do an ancient build,
instead of the current modern build. The downside of that is the ancient
build environment uses debian stable, so it has old versions of git,
libraries etc, that go into the build. --[[Joey]]