Package definition - argument, fix for wrong file format before unpack

[白い熊]

Hello everyone:

I'm trying to build some old apps - one of them is an emacs package only 
available now via the archive.org Wayback machine.

The problem is though that the download is an xxxx.tar.gz file in name - 
in fact it is really only a tar archive. So guix build fails with wrong 
file format error. Concretely - it is this file: 
https://web.archive.org/web/20110104020844/http://taiyaki.org/elisp/mell/src/mell-1.0.0.tar.gz

I think I should add some "(arguments" lines in the package recipe - 
replacing the unpack phase? However not sure exactly how - am searching 
but haven't found any examples fixing for such a problem.

Could someone advise me - how to specify the file should be unpacked as 
really just a tar archive so that the build can then proceed?

Many thanks.

--
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白い熊
ShiroiKuma