qrencode: fix build on x86_64-darwin

pkgs/development/libraries/qrencode/default.nix

···
-{ lib, stdenv, fetchurl, pkg-config, SDL2, libpng, libiconv }:
+{ lib, stdenv, fetchurl, pkg-config, SDL2, libpng, libiconv, libobjc }:
 
 stdenv.mkDerivation rec {
   pname = "qrencode";
···
   };
 
   nativeBuildInputs = [ pkg-config ];
-  buildInputs = [ SDL2 libpng ] ++ lib.optionals stdenv.isDarwin [ libiconv ];
+  buildInputs = [ SDL2 libpng ] ++ lib.optionals stdenv.isDarwin [ libiconv libobjc ];
 
   configureFlags = [
     "--with-tests"

pkgs/top-level/all-packages.nix

···
 
   qrcodegen = callPackage ../development/libraries/qrcodegen { };
 
-  qrencode = callPackage ../development/libraries/qrencode { };
+  qrencode = callPackage ../development/libraries/qrencode {
+    inherit (darwin) libobjc;
+  };
 
   geeqie = callPackage ../applications/graphics/geeqie { };