[openssl/openssl] 6cac1c: fix clang-6,7,8 strict build

[Marco Abbadini]

  Branch: refs/heads/master
  Home:   https://github.com/openssl/openssl
  Commit: 6cac1ce47128f5095b1f0b99f304589db034c305
      https://github.com/openssl/openssl/commit/6cac1ce47128f5095b1f0b99f304589db034c305
  Author: Marco Abbadini <marco.abbadini1 at gmail.com>
  Date:   2023-07-24 (Mon, 24 Jul 2023)

  Changed paths:
    M ssl/quic/quic_ackm.c

  Log Message:
  -----------
  fix clang-6,7,8 strict build

CLA: trivial

Reviewed-by: Kurt Roeckx <kurt at roeckx.be>
Reviewed-by: Paul Dale <pauli at openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21501)