gtk4.passthru.tests.pkg-config: Fix on Darwin

Previously it would fail with:

    ❌ pkg-config module gtk4-wayland was not found
    ❌ pkg-config module gtk4-x11 was not found

pkgs/development/libraries/gtk/4.x.nix

@@ -279,9 +279,13 @@ stdenv.mkDerivation (finalAttrs: {
     changelog = "https://gitlab.gnome.org/GNOME/gtk/-/raw/${finalAttrs.version}/NEWS";
     pkgConfigModules = [
       "gtk4"
+    ] ++ lib.optionals broadwaySupport [
       "gtk4-broadway"
+    ] ++ lib.optionals stdenv.hostPlatform.isUnix [
       "gtk4-unix-print"
+    ] ++ lib.optionals waylandSupport [
       "gtk4-wayland"
+    ] ++ lib.optionals x11Support [
       "gtk4-x11"
     ];
   };