Bug#1131881: want way to supporess dpkg-genchanges missing package warning

Package: dpkg-dev
Version: 1.22.22
Control: block 1131609 by -1

In tag2upload, we see warnings like this from dpkg-genchanges:

> >> Appending 'hippotat_1.3.2.git.tar.xz net optional' to debian/files
> dpkg-genchanges: warning: package hippotat-client in control file but not in files list
> dpkg-genchanges: warning: package hippotat-server in control file but not in files list
> dpkg-genchanges: warning: package hippotat-common in control file but not in files list

The reason for this seems to be the `.git.tar.xz` file, which is a
bundle of git stuff which forms part of our agreement with the ftp
archive team.

This causes dpkg-genchanges to no longer consider the upload
source-only, and instead it complains about all the missing binaries.

Empirically, passing `-S` to dpkg-genchanges causes it to omit the
.git.tar.gz, which is also wrong.

Could this warning please be suppressed, somehow, or made suppressable?
A tag2upload-specific option would be fine, or an option to suppress
this specific warning.  Alternatively, special handling of the
`.git.tar.xz` would be a possibility.

NB that the .git.tar.xz forms part of the upload (ie is mentioned in
.changes) but not part of the source package (so is not mentioned in
the .dsc).

I think ideally we would like this fix to be backported to stable-bpo.
The tag2upload builder uses dpkg-dev from stable, and I don't think we
want to change that.

Thanks,
Ian.