Perl 5.20, as any other new perl version, requires all modules that are not purely perl code to be rebuilt. We did that for all packages in our repos.
The last couple major updates printed an error message when trying to load modules built against the wrong version, 5.20 seems to cause segfaults. Please make sure to rebuild all custom installed CPAN modules and binaries that link to libperl.so.
Refer to post on arch-dev-public for a script that helps to find those packages.