[openssl/openssl] ac21c1: VMS knows POSIX threads too!

[Richard Levitte]

  Branch: refs/heads/master
  Home:   https://github.com/openssl/openssl
  Commit: ac21c1780a63a8d9a3a6217eb52fe0d188fa7655
      https://github.com/openssl/openssl/commit/ac21c1780a63a8d9a3a6217eb52fe0d188fa7655
  Author: Richard Levitte <levitte at openssl.org>
  Date:   2023-03-06 (Mon, 06 Mar 2023)

  Changed paths:
    M crypto/thread/arch/thread_posix.c
    M include/internal/thread_arch.h

  Log Message:
  -----------
  VMS knows POSIX threads too!

include/internal/thread_arch.h didn't indicate this, now it does.

This also removes ossl_crypto_mem_barrier(), because we isn't used
anywhere, and doesn't build with compilers that don't support the GNU
extension __asm__.

Reviewed-by: Matt Caswell <matt at openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit at gmail.com>
(Merged from https://github.com/openssl/openssl/pull/20440)