RFA: Use _Unwind_Ptr (Was: Re: RFC / RFA: dwarf2 unwinding for targets with call-part-clobbered registers)

[Joern Rennecke]

> _Unwind_Word
> _Unwind_GetGR (struct _Unwind_Context *context, int index)
> {
>   int uw_index = DWARF_REG_TO_UNWIND_COLUMN (index);
>   int size = dwarf_reg_size_table[index];

Actually, this needs to use uw_index too.

Also, I need to do a similar check when I set tmp_sp / sp_slot.
I'm working on making this into a separate inline function.

It will also require to have a dwarf_reg_size_table for the
stack pointer coloumn just like for any ordinary register.
With the currently pending patch, that means I'll have to
make sh.h tell that the stack pointer is partly call clobbered
for TARGET_SHMEDIA32 to get the right size.