Comment # 1 on bug 1212432 from Clifford Dugal

While more of a hack, I've at least been able to work around the issue by
changing line 2374 of /usr/sbin/dkms to read:

    weak_modules_no_initrd=""

I'm not sure if that results in any other issues, but I can at least
build/install the system76-io module after altering dkms in that way.