unzip: Fix build with gcc-15

pkgs/by-name/un/unzip/package.nix

@@ -86,6 +86,11 @@ stdenv.mkDerivation rec {
       sha256 = "67ab260ae6adf8e7c5eda2d1d7846929b43562943ec4aff629bd7018954058b1";
     });
 
+  # gcc-15 uses c23 standard, which removed non-prototype function declarations.
+  postPatch = ''
+    sed -i '/localtime()/ d' unix/unxcfg.h
+  '';
+
   nativeBuildInputs = [ bzip2 ];
   buildInputs = [ bzip2 ] ++ lib.optional enableNLS libnatspec;