dev-libs/cloog: drop to ~arm64

dev-libs/cloog: drop to ~arm64

Only gcc-4 and older needs this with USE=graphite, which was always
p.use.masked fully. This p.use.mask has been dropped, but gcc-5 does
not need cloog and older gcc are p.masked fully with the arch-specific
p.use.mask of graphite for <gcc-5 kept as well.
Instead of catching up in stable version with other architectures,
drop all to ~arm64 instead as per above.

Package-Manager: Portage-2.3.28, Repoman-2.3.9