After chrooting and configuring the "gentoo-sources" kernel manually the compilation (make && make modules_install) fails with Perl cannot be found. Its easy enough to fix just by a simple "emerge dev-lang/perl" after which the kernel compiles fine. The (amd64) "Handbook" doesn't mention installing Perl and maybe should just for the sake of thoroughness.
that's a bug on your side. can't reproduce -- this should never happen in anything approaching a normal system installation.
Actually, this is because the kernel needs perl to build but does not specify a dependency on it. *** This bug has been marked as a duplicate of bug 421483 ***