[openssl/openssl] c8a9b2: remove extra define for __NR_getrandom and add som...

[zzl-360]

  Branch: refs/heads/master
  Home:   https://github.com/openssl/openssl
  Commit: c8a9b26d6ed7a62d26a013c21e62ba4a0a2d6dd1
      https://github.com/openssl/openssl/commit/c8a9b26d6ed7a62d26a013c21e62ba4a0a2d6dd1
  Author: zhangzhilei <zhangzhilei at 360.cn>
  Date:   2023-01-06 (Fri, 06 Jan 2023)

  Changed paths:
    M providers/implementations/rands/seeding/rand_unix.c

  Log Message:
  -----------
  remove extra define for __NR_getrandom and add some comments

Reviewed-by: Tomas Mraz <tomas at openssl.org>
Reviewed-by: Kurt Roeckx <kurt at roeckx.be>
Reviewed-by: Hugo Landau <hlandau at openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19985)