Sorry for the delay :p

> In any case you can change (%current-system) to:
>
>   (or (%current-target-system) (%current-system))
>
> ...and it should work.  Feel free to push this change to 'master' :-)

OK, I could do that.
Now I'm trying to build a i686-linux mesa on a x86_64, but the following

--8<---------------cut here---------------start------------->8---
(define-public (to32 package64)
  "Build package for i686-linux.
Only x86_64-linux and i686-linux are supported.
- If i686-linux, return the package unchanged.
- If x86_64-linux, return the 32-bit version of the package."
  (match (%current-system)
    ("x86_64-linux"
     (package
       (inherit package64)
       (name (string-append (package-name package64) "32"))
       (arguments `(#:system "i686-linux"
                    ,@(package-arguments package64)))))
    (_ package64)))

(define mesa32
  (package
    (inherit (to32 mesa))
    (arguments
     (substitute-keyword-arguments (package-arguments mesa)
       ((#:phases phases)
        `(modify-phases ,phases
           (add-after 'unpack 'cross-disable-failing-test
             (lambda _
               (substitute* "src/gallium/tests/unit/meson.build"
                 (("'u_format_test',") ""))
               #t))))))))
--8<---------------cut here---------------end--------------->8---

still produces a x86_64 build of mesa.  Any clue what I'm missing?

-- 
Pierre Neidhardt
https://ambrevar.xyz/