[build] Move MD_UNWIND_SUPPORT to toplevel libgcc

[Paolo Bonzini]

On 07/05/2011 01:52 PM, Rainer Orth wrote:
> Instead of nested cases, I'd rather use one i[34567]86-*-linux* case and
> another for the rest, duplicating extra_parts and tmake_file.  Same for
> x86_64-*-linux* vs. the rest.
>
> But that's just me.

I agree.

Paolo