RFC: split ColdFire from m68k backend

[Giovanni Bajo]

Andreas Schwab wrote:

>>> I wouldn't mind having a modernized m68k backend. :-)
>>
>>   What things have to be changed to modernized the m68k backend?
>
> One thing that would be nice to have is to convert the
> prologue/epilogue to RTL.

Also, m68k is the major cc0 target at the moment. Making it drop cc0 support
would help cleaning up the compiler. You can ask Kazu Hirata, as he lately
modified h8300 to drop cc0.

Giovanni Bajo