Portage/Dependency.hs: allow simplification phase return 'AnyOf'

scion-browser had a 'zlib, zlib == 0.5.*' depend and failed as:
    ...
    Writing scion-browser-0.2.14.ebuild
    hackport: Portage/Dependency.hs: dev-haskell/zlib: unsolvable constraints

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>