Reference packages are to be removed as per bug 746962 Please move to use virtual implementations.
Resolved by cleanup: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=e894c12c617db62802e96461c177a43a5924b800 https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=3c1383564027115def71268d0c5ce43fe0dd147e https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=d7b6134c1f09b96526fb1ddbf9dfa7eb2e121987