Updated gmp to 6.1.2.

Changes between GMP version 6.1.1 and 6.1.2

  BUGS FIXED
  * Mini-GMP: Fixed a division bug, which on a machine with 64-bit
    unsigned long affects approximately 1 out of 2^32 divisors.

  * Mini-GMP: Fix mpz_set_str crash on inputs with a large number of
    leading zeros. Also stricter input validation, rejecting inputs
    with no digits.

  FEATURES
  * Handle more systems which require PIC code in static libraries (e.g.,
    "hardened" Gentoo and Debian 9).

  * Configuration for arm (-32 and -64) has been rewritten, fixing poor
    code selection for many CPUs.

  * Mini-GMP: Updated to the latest development version, including
    new functions mpn_com and mpn_neg.

  SPEEDUPS
  * None, except for arm CPUs affected by the configuration rewrite.

(wiz)