diebahn: fix build on Darwin

* Include required frameworks; and
* Use gettext from nixpkgs (required for building with newer clangs).

pkgs/applications/misc/diebahn/default.nix

···
 , gtk4
 , libadwaita
 , pango
+, gettext
 , darwin
 }:
 
···
     gtk4
     libadwaita
     pango
-  ] ++ lib.optionals stdenv.isDarwin [
-    darwin.apple_sdk.frameworks.Security
-  ];
+  ] ++ lib.optionals stdenv.isDarwin (with darwin.apple_sdk.frameworks; [
+    CoreFoundation
+    Foundation
+    Security
+  ]);
+
+  # Darwin needs to link against gettext from nixpkgs instead of the one vendored by gettext-sys
+  # because the vendored copy does not build with newer versions of clang.
+  env = lib.optionalAttrs stdenv.isDarwin {
+    GETTEXT_BIN_DIR = "${lib.getBin gettext}/bin";
+    GETTEXT_INCLUDE_DIR = "${lib.getDev gettext}/include";
+    GETTEXT_LIB_DIR = "${lib.getLib gettext}/lib";
+  };
 
   meta = {
     description = "GTK4 frontend for the travel information of the german railway";