While I pass to it a specific commit, it downloads a different
(older?) version. I have prepared a testcase with the libpthread,
which is the one that this happens. It will download the files and
then the building will fail, so just compare the file
sysdeps/mach/hurd/pt-sysdep.h with the same file from the commit
e2ae1c43d168fc6f8b34332cbb0656e5d107cbf3 in master. They are
different.

Build it with "./pre-inst-env guix build libpthread -K"