pngnq: fix with gcc 14

Various includes are missing.
The zlib include was being patched in before.
The string include is now needed with gcc 14.

pkgs/by-name/pn/pngnq/missing-includes.patch

@@ -0,0 +1,17 @@
+diff --git a/src/rwpng.c b/src/rwpng.c
+index aaa21fc..11d698f 100644
+--- a/src/rwpng.c
++++ b/src/rwpng.c
+@@ -30,10 +30,12 @@
+   ---------------------------------------------------------------------------*/
+ 
+ #include <stdio.h>
++#include <string.h>
+ #include <stdlib.h>
+ 
+ #include "png.h"        /* libpng header; includes zlib.h */
+ #include "rwpng.h"      /* typedefs, common macros, public prototypes */
++#include <zlib.h>
+ 
+ /* future versions of libpng will provide this macro: */
+ /* GRR NOTUSED */

pkgs/by-name/pn/pngnq/package.nix

@@ -16,16 +16,20 @@ stdenv.mkDerivation rec {
     sha256 = "1qmnnl846agg55i7h4vmrn11lgb8kg6gvs8byqz34bdkjh5gwiy1";
   };
 
+  patches = [
+    ./missing-includes.patch
+  ];
+
+  env.NIX_CFLAGS_COMPILE = toString [
+    "-Wno-error=incompatible-pointer-types"
+  ];
+
   nativeBuildInputs = [ pkg-config ];
   buildInputs = [
     libpng
     zlib
   ];
 
-  patchPhase = ''
-    sed -i '/png.h/a \#include <zlib.h>' src/rwpng.c
-  '';
-
   meta = with lib; {
     homepage = "https://pngnq.sourceforge.net/";
     description = "PNG quantizer";