Bug#145257: [britney] build-depends not taken into consideration for arch:all packages

[Graham Inggs <ginggs@debian.org>]

Some recent bugs that seem to have been caused by this:

#898245 src:flask-limiter    -> python-aniso8601
#932507 src:python-crontab    -> python-croniter
#932509 src:pyrsample        -> python-xarray