icoutils: fix build on aarch64-darwin

pkgs/tools/graphics/icoutils/default.nix

···
   buildInputs = [ libpng perl ];
   propagatedBuildInputs = [ perlPackages.LWP ];
 
+  # Fixes a build failure on aarch64-darwin. Define for all Darwin targets for when x86_64-darwin
+  # upgrades to a newer SDK.
+  NIX_CFLAGS_COMPILE = lib.optional stdenv.isDarwin "-DTARGET_OS_IPHONE=0";
+
   patchPhase = ''
     patchShebangs extresso/extresso
     patchShebangs extresso/extresso.in