Good catch!

It also does the trick for generic-cl:

--8<---------------cut here---------------start------------->8---
(arguments
 `(#:tests? #f
   #:phases
     (modify-phases %standard-phases
       (add-after 'unpack 'fix-compile-order
         (lambda _
           (substitute* "generic-cl.asd"
             ((":module \"src\"") ":module \"src\" :serial t")))))))
---------------cut here---------------end--------------->8---

I don't understand why it works outside our build system.
It works when I run SBCL locally, so technically with the same ASDF.

I'll ask upstream, maybe they have a clue.

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