This was already addressed in POSIX.pm and Perl 5.004_02 - Compatible?. Maybe an analogy is in order.

If you take apart a clock, you end up with a whole lot of small parts. What you are trying to do is put a small part (POSIX.pm) into another clock (your perl installation), without knowing whether that part originally belonged to the clock, is already in there, misses any other parts that it needs in order to work. etc. etc.

Get a whole, working clock in one piece. It will have all the right parts.

Liz