[openssl/openssl] c2dbf9: BN_gcd(): Avoid shifts of negative values

[Tomáš Mráz]

  Branch: refs/heads/openssl-3.0
  Home:   https://github.com/openssl/openssl
  Commit: c2dbf9ef1f9cc26c5fb1540393a89a56b2469d91
      https://github.com/openssl/openssl/commit/c2dbf9ef1f9cc26c5fb1540393a89a56b2469d91
  Author: Tomas Mraz <tomas at openssl.org>
  Date:   2023-10-05 (Thu, 05 Oct 2023)

  Changed paths:
    M crypto/bn/bn_gcd.c

  Log Message:
  -----------
  BN_gcd(): Avoid shifts of negative values

Fixes #22216

Thanks to Leland Mills for investigation and testing.

Reviewed-by: Tom Cosgrove <tom.cosgrove at arm.com>
Reviewed-by: Matt Caswell <matt at openssl.org>
Reviewed-by: Paul Dale <pauli at openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22272)

(cherry picked from commit 0f7a3b0caa33a87c900536dc1c02fa553d2193cc)