chromium: Use system protobuf for versien 25.

This should at least mitigate our build error to only occur in v8 anymore.
Unfortunately we can't use v8 from nixpkgs right now, so we're going to put out
our sledgehammer in the next commit. Meanwhile, it doesn't hurt to get rid of
the bundled protobuf library, so let's do it.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
chromium: Force -fno-stack-protector for v25.

So, this is our sledgehammer, forcing -fno-stack-protector for every gcc/g++ in
the univ... Chromium build. Of course this is a somewhat nasty fix and there
should be a real fix somewhere in Chromium 26. But instead of wandering around
and picking cherries, we now go out for the slaughter until someone brings us
the damn cherries because we are FUURRRIII... no well... time for sleep :-)

May the mighty Hydra be with us!

Thanks to our great fellow @cillianderoiste, for joining the battle with his
almighty battle axe, crushing and burning some CPUs.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
Tested-by: Cillian de Róiste <cillian.deroiste@gmail.com>