gdk-pixbuf: fix binary @rpath reference on darwin

pkgs/development/libraries/gdk-pixbuf/default.nix

@@ -82,6 +82,11 @@ stdenv.mkDerivation rec {
       $dev/bin/gdk-pixbuf-query-loaders --update-cache
     '';
 
+  # The fixDarwinDylibNames hook doesn't patch binaries.
+  preFixup = stdenv.lib.optionalString stdenv.isDarwin ''
+    install_name_tool -change "@rpath/libgdk_pixbuf-2.0.0.dylib" "$out/lib/libgdk_pixbuf-2.0.0.dylib" $out/bin/gdk-pixbuf-thumbnailer
+  '';
+
   # The tests take an excessive amount of time (> 1.5 hours) and memory (> 6 GB).
   inherit doCheck;