As carrier-grade NATs are becoming common, many players cannot host
Clonk games at all. The simple STUN-like netpuncher from Clonk Rage
which was removed three years ago is already effective against some
DS-Lite NATs.
With some extensions, we should be able to make it work with more
restrictive NATs as well.
This reverts commit 72002cc366.
Another piece of code that hasn't been tested in ages, gone. The default
puncher address was still pointing to clonk.de, which I'm very certain
isn't providing UDP hole punching services anymore.
Instead of a bespoke hole punching implementation we should use a STUN
lib.
NativeToolsExport.cmake gets generated in non-cross builds so potential
cross builds later know where to find a native c4group.
Ignore it so in-tree builds don't accidentally commit it.