Stable package x11-base/xorg-proto currently has RDEPEND !<x11-proto/scrnsaverproto-1.2.2-r2
Your problem is fixed with https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=cb05bc69b8ff9faafeedcc0aeb733761285d4bc0 *** This bug has been marked as a duplicate of bug 651286 ***