virtual/perl-Switch depends on =dev-lang/perl-5.12* or its perl-core name equivalent. With perl-5.16 being stable, virtual/perl-Switch now tries to pull in perl-5.12 since perl-core/Switch is not stable on amd64. My suspicion is that the dep should be >=dev-lang/perl-5.12, since upstream mentions it's maintained by the perl mongers as part of perl core.
Switch.pm is not provided by Perl itself beyond 5.13.0 -- corelist -a Switch Data for 2013-12-20 Switch was first released with perl v5.7.3, deprecated (will be CPAN-only) in v5.11.0 and removed from v5.13.1 v5.7.3 2.06 v5.8.0 2.09 v5.8.1 2.10 v5.8.2 2.10 v5.8.3 2.10 v5.8.4 2.10 v5.8.5 2.10 v5.8.6 2.10 v5.8.7 2.10 v5.8.8 2.10_01 v5.8.9 2.13 v5.9.0 2.10 v5.9.1 2.10 v5.9.2 2.10 v5.9.3 2.10_01 v5.9.4 2.10_01 v5.9.5 2.13 v5.10.0 2.13 v5.10.1 2.14 v5.11.0 2.14_01 v5.11.1 2.15 v5.11.2 2.16 v5.11.3 2.16 v5.11.4 2.16 v5.11.5 2.16 v5.12.0 2.16 v5.12.1 2.16 v5.12.2 2.16 v5.12.3 2.16 v5.12.4 2.16 v5.12.5 2.16 v5.13.0 2.16 -- Thus, the || ( ) conditional means to say: - If you're on perl 5.12, use perl 5.12 - Otherwise, install perl-core/Switch perl-core/Switch exists. So it seems perl-core/Switch needs to be stabilised due to the removal of <perl-5.13
*** This bug has been marked as a duplicate of bug 511874 ***
