[bug#67506] guix: platform: Add platform-rust-architecture.

[Jean-Pierre De Jesus Diaz]

Hello,

The patch series looks good to me.  I was thinking of something
similar to this in order
to add a procedure to cross compile the `std` target so that the rust
package can use it.

I was thinking that maybe the RUST-ARCHITECTURE could be called RUST-TARGET and
that it could be a list (RUST-TARGETS) as some GCC multilib targets
don't have a single
RUST-TARGET, namely arm-none-eabi and avr, but the latter only has one
rust target
but the intention from the existing target is to add more as needed I
think, as the
avr-unknown-gnu-atmega328 target is MCU specific.

But given that there are zero multilib targets present in GNU Guix as
of now I think
it can stay as a string.

Cheers,

-- 
Jean-Pierre De Jesus DIAZ
Foundation Devices, Inc.