zgv: fix GCC 14 build

pkgs/applications/graphics/zgv/add-include.patch

@@ -0,0 +1,11 @@
+diff --git a/src/modesel.c b/src/modesel.c
+--- src/modesel.c
++++ src/modesel.c
+@@ -6,6 +6,7 @@
+  */
+ 
+ #include <stdio.h>
++#include <stdlib.h>
+ #include "zgv_io.h"
+ #include "readnbkey.h"
+ #include "modesel.h"

pkgs/applications/graphics/zgv/default.nix

@@ -35,6 +35,7 @@ stdenv.mkDerivation rec {
   ];
 
   patches = [
+    ./add-include.patch
     (fetchpatch {
       url = "https://foss.aueb.gr/mirrors/linux/gentoo/media-gfx/zgv/files/zgv-5.9-libpng15.patch";
       sha256 = "1blw9n04c28bnwcmcn64si4f5zpg42s8yn345js88fyzi9zm19xw";