gmp: 5.1.3 - bug fix updates for gmp library

I've commented out the bottle info as I can't provide the bottled versions. This is a minor bugfix update.

Changes between GMP version 5.1.2 and 5.1.3

BUGS FIXED
  * The internal functions mpn_sbpi1_div_qr_sec mpn_sbpi1_div_r_sec could compute garbage with a low probability.  They are now rewritten, and the test code has been improved.

  * A bug in the ia64 implementation of mpn_divrem_2, clobbering some callee-save registers, has been fixed. This is an internal function, with the bug manifesting itself as miscomputation in, e.g., mpn_sqrtrem.

  * The documentation now correctly says 'const' for input arguments.