Update to 5.1.2:

Changes between GMP version 5.1.1 and 5.1.2

  BUGS FIXED
  * A bug in mpz_powm_ui triggered by base arguments of at least 15000 decimal
    digits or mod arguments of at least 7500 decimal digits has been fixed.

  * A AMD Bulldozer specific bug affecting the 64-bit Windows ABI has been
    fixed.  This bug was in a key function (mpn_mul_1) and made both Bulldozer
    specific builds and fat builds run on Bulldozer completely non-functional.

  MISC
  * Fixes and generalisations to the test suite.

  * Minor portability enhancements.
Updated devel/gmp to 5.1.2