[RFC] .debug_frame adjustments for mips-irix

[Eric Christopher]

> 
>  Humm, my understanding was that this only pushes a DW_CFA_register into the
>  CIE, and that we also need a DW_CFA_offset statement for the return-address
>  virtual column into the FDE when we save the return address register. Those
>  bits were specifically intended for the latter.

Hrm, I think you're right. I was just trying to avoid the extra code in
mips.c. Of course, afaict, mips-irix is the only port to do this for the
unwinder so more generic code wouldn't have been written.

If that's the only way to do it then I'm fine with it.

-eric