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sub is_suffix { substr($_[0], -length($_[1])) eq $_[1] }

...
    $_[0] =~ m[(?>(.+))(?(?{ not is_suffix($_[1], $^N) })(?!))]s;
    return $1;
}

use List::Util qw/ reduce /;

...

__END__
all

sub common_suffix {
    $_[0] =~ m[
...
    ]xs;
    return $1;
}