bug#66866: aarch64 system cross compilation + pinebook pro image broken?

[dan]

with git bisect i found after this commit the cross-compilation 
couldn't work anymore:
http://git.savannah.gnu.org/cgit/guix.git/commit/?id=1328c4cca531318e3ed90c6aecb522a5b22a4bcc

i think this is beyond my ability to understand why it breaks, but 
if anyone could take a look at this it would be really helpful.
--
dan