Backports needed for Firefox/Thunderbird ESR 78 in Buster/Stretch

[Moritz Muehlenhoff]

On Wed, Sep 02, 2020 at 05:25:28AM +0900, Mike Hommey wrote:
> Note Firefox doesn't need wasi-libc at the moment. Neither does
> thunderbird AFAICT.

Not Firefox/Thunderbird itself, but rustc in the versions needed by ESR 78
build depends on it.

Cheers,
        Moritz