[3.0.x] Build failure with stricter C compilers (e.g. GCC 14)

Modern C compilers are becoming stricter with a variety of changes over the last year or so.

GCC 14 in particular (to be released in ~April 2024) fails to build vlc-3.0.20 like:

input/es_out.c: In function ‘EsOutControlLocked’:
input/input.c: In function ‘InitTitle’:
input/input.c:910:19: error: assignment to ‘const input_title_t **’ from incompatible pointer type ‘input_title_t **’ [-Wincompatible-pointer-types]
  910 |     priv->title   = p_master->title;
      |              

Originally reported downstream in Gentoo at https://bugs.gentoo.org/919068.

This can be emulated with -Werror=incompatible-pointer-types -Werror=implicit -Werror=int-conversion on an older GCC or Clang.