bug#54864: GNU Cuirass reports arm64 as armhf

[Mathieu Othacehe]

Hello,

> I've had this experience before, it's very confusing (it goes on trying
> to build a toolchain for something that is sure to fail).  Perhaps we
> could at least have a place to refer to in the manual for the common GNU
> triplets which make the most sense in for GNU Guix (e.g., the currently
> supported GNU system triplets).  Currently I grep the manual for
> disparate examples when my memory fail me.

Yes, I also cannot remember those triplets even though I'm
cross-compiling all day long.

Maybe we could:

* Define all the supported architectures in (gnu platforms). We already
  have ARM and Hurd defined there.

* Define %supported-systems and %supported-targets lists constructed by
  parsing the <platform> records.

* Use those lists to check the values passed to --system and --target
  arguments.

* Add --list-available-systems and --list-available-targets arguments
  for all the commands supporting --system and --target arguments.

WDYT?

In the meantime we can close that one I guess.

Thanks,

Mathieu