dev-db/virtuoso-odbc-6.1.8 cannot be emerged because it fails to download VOS-genpatches-6.1.8.tar.bz2
Please don't use mirror://gentoo for distributing these patches. Use your dev space and adjust virtuoso eclass accordingly. The mirrors are no reliable source as you can see with this bug.
virtuoso has usually used the mirrors, I just forgot to actually upload the tarball. Since the SRC_URI is set in eclass, we can't use devspace. My fault, fixed on dev.gentoo.org, give it a couple hours to hit mirrors. Reopen if there are further problems.