PPC startup code

[Roland McGrath]

> However, you still need to provide compatibility code so that
> executables that contain the old crt1.o can still run.  In practise,
> this means that changing an ABI just to "clean up glibc" doesn't work;
> things just get worse because now you have both the old ABI *and* the
> new ABI to support.

That burden is limited, and not really worse because it's just the same
source code we have now as private function and a public function, made
into a new-versioned public function and an old-versioned compatibility
function that in some future configuration won't be compiled in.