Implement the weak aliases for private entry points in the inet_*

Implement the weak aliases for private entry points in the inet_*
and res_* modules in a way that works for ELF.  I moved the aliases
out of res_stubs.c and into the individual modules where the entry
points are defined.  Weak aliases don't work in ELF unless that is
the case.  (Actually, I'm surprised it worked for a.out.)

This should fix the undefined "inet_addr" and related symbols in
various applications that fail to include <arpa/inet.h> or
<resolv.h> as they are supposed to do.