[InterNetNews/inn] 7780a6: Add new warnings from GCC 13

[Julien ÉLIE]

  Branch: refs/heads/main
  Home:   https://github.com/InterNetNews/inn
  Commit: 7780a66d76bdeca676be31b28042df69dd723844
      https://github.com/InterNetNews/inn/commit/7780a66d76bdeca676be31b28042df69dd723844
  Author: Julien ÉLIE <Julien-Elie at users.noreply.github.com>
  Date:   2024-02-11 (Sun, 11 Feb 2024)

  Changed paths:
    M configure.ac

  Log Message:
  -----------
  Add new warnings from GCC 13

Enable -fstrict-aliasing -fstrict-flex-arrays=3 -Wformat-signedness
-Warray-bounds=3 -Wuse-after-free=3

Also silent two warnings from Clang: -Wno-unsafe-buffer-usage
-Wno-reserved-identifier