Hello Guix!

In an optimistic attempt to eventually have Icecat on a Pinebook Pro, I
thought I'd try and get rust building on aarch64. Here's a fix for the
post-install phase that had an x86 triplet hardcoded. With this we're
able to start off the bootstrap chain!

That being said, each step takes ~5 hours on this machine so this is
going to take a while :-), it's currently working on 1.23.

So, I suppose this should go into either core-updates or staging? WDYT?

Thanks!
Pierre