According to Kostas Magoutis <magoutis@eecs.harvard.edu>:
> #include <unistd.h>
> 
> main()
> {
>         int p;
> 
>         p = vfork();
> }
> 
> compiled using gcc -D__ELF__ test.c results in
> 
> Undefined symbol `__vfork14' referenced from text segment
> 
> Compiling without the __ELF__ links okay.

You need an elf compiler to produce elf code. Definining __ELF__ does
not magically change the compiler. The reason you see the undefined
symbol is that libc is still a.out and has an extra underscore.
What are you trying to do? If you are trying to upgrade to /current
get a snapshot.

christos