Log Message:
Update gmp to 6.1.0:

Changes between GMP version 6.0.* and 6.1.0

  BUGS FIXED
  * The public function mpn_com is now correctly declared in gmp.h.

  * Healed possible failures of mpn_sec_sqr for non-cryptographic sizes for
    some obsolete CPUs.

  * The option --disable-assembly now disables all inlined asm.

  * Fixed bug affecting mini-gmp's bitwise functions mpz_setbit, mpz_clrbit,
    and mpz_combit.

  * Various problems related to precision for mpf have been fixed.

  * Fixed ABI incompatible stack alignment in calls from assembly code.

  * Fixed PIC bug in popcount affecting Intel processors using the 32-bit ABI.

  SPEEDUPS
  * Speedup for Intel Broadwell and Skylake though assembly code making use of
    new ADX instructions.

  * Square root is now faster when the remainder is not needed. Also the speed
    to compute the k-th root improved, for small sizes.

  * Improved arm64 support.

  FEATURES
  * New C++ functions gcd and lcm for mpz_class.

  * New public mpn functions mpn_divexact_1, mpn_zero_p, and mpn_cnd_swap.

  * New public mpq_cmp_z function, to efficiently compare rationals with
    integers.

  * Support for Darwin in all x86 code, thereby enabling fat builds on Darwin.

  * Support for more 32-bit arm processors.

  * Support for compilation with clang/llvm on more platforms.  Caution: GMP
    triggers mis-compilation bugs in clang for many platforms, such as arm, x86
    (32-bit and 64-bit), powerpc, mips.

  * Support for AVX-less modern x86 CPUs. (Such support might be missing either
    because the CPU vendor chose to disable AVX, or because the running kernel
    lacks AVX context switch support.)

  * Stack usage trimmed; we believe 512 KiB is now sufficient for any GMP
    call, irrespective of operand size.

  * Support for NetBSD under Xen; we switch off AVX unconditionally under
    NetBSD since a bug in NetBSD makes AVX fail under Xen.

  MISC
  * We now use manufacturers' code names for x86 CPUs, e.g., "haswell" \ 
instead
    of names derived from the commercial brands.

  * Small improvements and better coverage for the test suite.

  * The various FreeBSD problems listed for 6.0.0 affect this release too.

  * Tuned values for FFT multiplications are provided for larger number on
    many platforms.