> version will be very slow if there are only negative numbers... ;)

eh eh, you are right but the check does not slow it at all..

Discipulus => sub{
        my @list = sort {$a<=>$b} @input;
        if ($list[0] < 0 and $list[-1] > 0){
            push @list, shift @list until $list[0] >= 0;
        }
        Compare(\@list,\@output) or die "@list" if DO_CHECK;
    },
[download]

update: more test cases.. more checks!

Discipulus4 => q{ # https://www.perlmonks.org/?node_id=1229437
        @list = sort {$a<=>$b} @list;
        if ($list[0] < 0 and $list[-1] >= 0)
            { push @list, shift @list until $list[0] >= 0 }        },
[download]