dev-lang/gnat-3.14p.ebuild tries to fetch files under http://gd.tuwien.ac.at/languages/ada/gnat/3.14p/ which are no longer available. Instead, server.php?GD.TUWIEN.AC.AT* is fetched and stored in gentoo distfiles mirror server. If you have those files on your machine, please put it on dev.gentoo.org.
Done