Log Message:
gmp: update to 6.2.1.

Fix some pkglint while here.

Changes between GMP version 6.2.0 and 6.2.1

  BUGS FIXED
  * A possible overflow of type int is avoided for mpz_cmp on huge operands.

  * Overflows are more carefully detected and reported for mpz_pow_ui.

  * A bug in longlong.h for aarch64 sub_ddmmss, not affecting GMP, was healed.

  * mini-gmp: mpz_out_str and mpq_out_str now correctly handle out of
    range bases.

  FEATURES
  * C90 compliance.

  * Initial support for Darwin on arm64, and improved portability.

  * Support for more processors.

  SPEEDUPS
  * None, except indirectly through recognition of new CPUs.