* Remove armhf from architecture list for qtwebengine build-dep,
we don't have (and may never have) it in Raspbian.
* Remove armhf from architecture list for gpsbabel-gui, it
needs the aforementioned build-dep.
* Try and fixup clean target in debian/rules it seems
that on systems where the gui can't be built the upstream
build process generates a broken gui/Makefile.