Including <limits.h> in gmp-impl.h

[Torbjorn Granlund]

Marc Glisse <marc.glisse at inria.fr> writes:

  I couldn't find anything other than the -mcpu=ultrasparc ABI=32 issue
  with gcc-2.9x around 1999-2000.

I haven't looked deeply into this issue, but to me it seems strange that
we define INT_MAX etc ourselves.

I think we might trust limits.h these days.  If a 15 year old system
then gets desupported, too bad.

Alternatively (or in some combo) we could define and use GMP_INT_MAX
(etc).

Torbjörn
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