r189535 - Add missing definitions to unwind.h.

[Rafael Espíndola]

> The problem is that if we use _Unwind_GetIP from unwind.h, we fail to
> link because the symbol is not defined in libgcc on Android.
>
> It seems that libgcc provides inline definitions of these functions
> (it uses macros actually), so maybe that's what we should do? I've
> attached a patch, but would need someone more experienced to look at
> it since I'm not familiar with these functions.

Yes, it looks like we have to do something equivalent to what the gcc one does.

Just two comments:

* _Unwind_GetIPInfo is the same in both #ifdef branches, just keep it out of it.
* Can you check if darwin arm has declarations or definitions? If
declarations, we should probably also only have declarations in that
case.

Cheers,
Rafael