GMP 4.2 a disaster on Darwin

[Jack Howarth]

   It turns out that we can in fact build 32-bit libraries on Darwin
using the ABI=32 configure option in GMP 4.2. The resulting gmp
4.2 build passes all of its make check. Furthermore, I can use the
resulting libraries (with the proposed configure.in patch to gcc)
to build gfortran which passes all of its make check as well. So
this issue appears to be solved for Darwin.
          Jack