- in callstack_pop, we don't free arch_ptr.  That's because this doesn't
  get copied over the clone.  It's a mere coincidence that fork() doesn't
  need to save register arguments, and this works.

- added copyright notices to files that this touches.  This is based on
  git blame.  Only contributors of 10+ lines are added

- test suite adjusted to not include "void" type as "don't show this int".
  Back ends in general need to know the exact type, so this never worked
  anyway.