Updating the VAX GCC backend from cc0 to MODE_CC

[David Brownlee]

The gcc VAX backend is in danger of being dropped if it doesn't get
converted from the older cc0 to the newer MODE_CC implementation.

John Paul Adrian Glaubitz <glaubitz at physik.fu-berlin.de> has started a
bountysource entry
https://www.bountysource.com/issues/91495157-vax-convert-the-backend-to-mode_cc-so-it-can-be-kept-in-future-releases
and asked for people to post it anywhere it might be found
interesting, in case anyone would like to add to the bounty, or
collect it :)

(I find it quite amusing to it mixed in between entries like "Optimize
NumPy SIMD algorithms for Power VSX")

You could easily argue that modern gcc is too big to be practical to
run on a VAX anyway, but making practical a requirement for
classiccmp.org would rule out _so_ much fun stuff :)

Thanks

David