PPC: ensure_undef_dynamic on weak undef only in plt
It's slightly weird to have a call to a weak function not protected by
a test of that function being non-NULL, but the non-NULL test might be
covered by a test of another function. For example:
if (func1)
{
func1 ();
func2 ();
}
where func2 is known to exist if func1 exists.
* elf32-ppc.c (allocate_dynrelocs): Call ensure_undef_dynamic for
weak undefined symols that only appear on PLT relocs.
* elf64-ppc.c (allocate_dynrelocs): Likewise.