I can't paste the error because I just broke my loop devices and so can't
recreate it any more. But it was recreatable.
You get errors because it accesses these files:
/lib/modules/2.6.10-gentoo-r7/kernel/fs/squashfs/squashfs.ko
/etc/mtab
on these lines of the ebuild:
modprobe squashfs || ewarn "no squashfs modules - test not completed"
umount ${T}/squashfs_dir
The second can be fixed easily by passing -n to umount. The first requires you
to either skip the test if sandboxing is enabled, or addwrite (don't know how
that works though).
I've actually disabled the testing, sine it seemed easier to do then to
troubleshoot, and I personally don't have the time to perform a proper fix.
