gmp 6.2.0 build failure in 32-bit mode on Linux/mips

[Bruno Haible]

Niels Möller wrote:
> Please set "ABI" on the configure command line.

The manual https://gmplib.org/manual/ABI-and-ISA does not list any allowed
values for ABI on Linux/mips.

> Adding ABI-changing
> flags to CC causes confusion (even if it works fine with other packages,
> and possibly for gmp too *if* configured with --disable-assembly). Don't
> do that.

It is possible to determine the ABI from the $CC $CFLAGS variables [1].
For the distinction between the 3 ABIs on MIPS, two tests are needed at
configure time (works also when cross-compiling):

  #if defined _MIPS_SZLONG && (_MIPS_SZLONG == 64)  => then it's ABI=64
  #else
    #if (_MIPS_SIM == _ABIN32)  => then it's ABI=n32
    #else                       => then it's ABI=32

If you were to put this logic into the GMP configure, GMP would determine
the correct ABI to use in one more case. (It already does so in many cases.)

Bruno

[1] https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=blob;f=m4/host-cpu-c-abi.m4