Hello,
I'm helping Manolis forward some pending patches.
Attach the patch with suggested corrections.

Make sure the phase returns #t on success:

   (and (zero? (system* "make" …))
        (begin
          (copy-file …)
          #t))


> +    (synopsis "Microkernel of the GNU system")
> +    (description
> +     "GNU Mach is the microkernel upon which a GNU Hurd system is 
> based.")
> +    (license gpl2+)))

Does it build both on GNU/Linux and GNU/Hurd?

For GNU/Linux (core-updates) works, also works in Hurd.