[PATCH] support for mingw-w64

[Torbjorn Granlund]

Thanks for the GMP patch!

Comments:

* We unfortunately cannot use intptr_t unconditionally, since it is not
  available everywhere we want GMP to work; it is a C99 feature.

  I wonder if size_t could be used instead?  While perhaps not elegant,
  it should work.  Does anybody see any problem?

  (Alternatively, we could define our own little type, gmp_intptr_t
  which we set up in gmp-impl.h.  There are some precedents in that
  file.)

* Why is it necessarly to pass -std=c99 to gcc?

  Passing this flag to gcc might be a good idea for all configurations,
  but then it should better be done using a global feature test, perhaps
  via our _opt flags mechanism.  Setting a globally avaiblable flags for
  one platform seems wrong.

Did you write this patch yourself?  It is large enough to be covered by
copyright law, meaning that the GNU project needs paperwork from its
authors.  This is a few minutes of work, but we need to protect the
legal status of GMP for the benefit of its users.

-- 
Torbjörn