Various patches against gmp-4.3.0

[Torbjorn Granlund]

Marc Glisse <marc.glisse at normalesup.org> writes:

  I don't think so. But then again I didn't think there would be a
  problem without it. I am surprised nobody seems to have hit this
  problem before (MPIR has the same code there and no related bug report
  in their system, although they are supposed to compile for windows not
  only with cygwin).

The same goes for many of the problems reported together with this one.
  
  Bah, the extern "C" { ... } should not hurt.

Thanks, I've put it in.

-- 
Torbjörn