Also (re-)adds some debian armhf-patches – not really needed, but making
it easier to apply the libstdc++-related patches without having to
modify them.
Also: Grab dependencies, patches and further config options from ubuntu
upstream build sources. Builds statically against a
mozilla-gcc-7/libstdc++7. Let's hope this works for Appimages and
Flatpaks as well, "everywhere".
