Support for w*ndows

[Torbjorn Granlund]

Torbjorn Granlund <tg at gmplib.org> writes:

  We should add some configury mechanism that selects ready files, and
  ignores non-ready files.  I am not sure how to do this.

I did something similar to the mechanism for nails.  An assembly file
that supports more than the standard ABI need to provide ABI
declarations:

ABI_SUPPORT(DOS64)
ABI_SUPPORT(ELF64)

In configure, for environments that do not comply to the standard ABI,
we need to issue a statement declaration

  AC_SUBST(GMP_NONSTD_ABI,DOS64)

Finally, in the loop for selecting mpn code, when GMP_NONSTD_ABI is set,
files without the corresponding ABI_SUPPORT seclaration will be skipped.

Things seem to work well on a virtual dos64 machine around here.

-- 
Torbjörn