[build] Move unwinder to toplevel libgcc (v2)

[Rainer Orth]

Paolo Bonzini <bonzini@gnu.org> writes:

> Writing that down in a wiki page (even as unformatted text)  would be
> useful.

While I'm not too fond of WiKis, I've added some text to

	http://gcc.gnu.org/wiki/Top-Level_Libgcc_Migration

It's ugly right now, but better than nothing.

	Rainer

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Rainer Orth, Center for Biotechnology, Bielefeld University