Long double support on m68k

[Andrew Cagney]

> Yes (if they support the fpu at all).
> 
> |> So, if a target's raw FP registers are in the correct format for
> |> REGISTER_CONVERT* then they are also in the correct format for this change
> |> and such targets will continue to work.  If a target's raw FP registers
> |> were not in the correct format then, that target is already broken and
> |> this change doesn't make things better or worse.
> 
> Yes.  There is only one floating point format for the m68k fpu.  The
> previous version already assumed floatformat_m68881_ext, this patch just
> removes the conversion, and makes the raw format avaliable to gdb.


The other thing it affects is `sizeof (long double)`.  For GCC, at 
least, is m68k's `sizeof (long double)` 12?

	Andrew