gnulib has a long list of dependencies. Most of them look like they are
not actually required for using check-module or gnulib-tool. For
instance, gnulib-tool seems to work just fine without bison or gperf.
Looking at gnulib-tool, it seems like none of the dependencies is
required to run it. Would it be sensible to just move all (or most) of
them from Depends to Recommends?
The actual need behind that suggestion is that gnulib currently cannot
satisfy other packages' cross build dependencies, because it is not
marked Multi-Arch: foreign. As long as it depends on build-essential or
bison, it cannot be marked such. After demoting those dependencies to
Recommends, it can be marked.
 bison is currently wrongly marked Multi-Arch: foreign.