gmp 64 bit configure failure on Solaris/SPARC

[Norm Jacobs]

While building GNU MP 6.1.2 (and 6.1.1) with GCC 5[.4] on a current 
build of the Solaris release in development on a SPARC system, I ran 
across the following error while configuring gmp.

    $ ./configure CC=/usr/gcc/5/bin/gcc CFLAGS=-m64 ABI=64
    checking build system type... sparc-sun-solaris2.12
    checking host system type... sparc-sun-solaris2.12
    checking for a BSD-compatible install... /usr/gnu/bin/install -c
    checking whether build environment is sane... yes
    checking for a thread-safe mkdir -p... /usr/gnu/bin/mkdir -p
    checking for gawk... gawk
    checking whether make sets $(MAKE)... yes
    checking whether make supports nested variables... yes
    checking whether to enable maintainer-specific portions of Makefiles... no
    configure: error: ABI=64 is not among the following valid choices: 32

The following patch appears to resolve the issue and the tests run by 
'make check' pass.

    --- gmp-6.1.1/configure.ac.orig 2017-01-04 20:22:16.789422430 +0000
    +++ gmp-6.1.1/configure.ac      2017-01-04 20:47:35.488157345 +0000
    @@ -1318,7 +1318,7 @@
          # reject ABI=64 in favour of ABI=32 if the user has forced the flags to
          # 32-bit mode.
          #
    -    abilist="32"
    +    abilist="64 32"
          cclist="gcc acc cc"
          any_testlist="sizeof-long-4"
          GMP_INCLUDE_MPN(sparc32/sparc-defs.m4)

   -Norm