Merge pull request #227018 from wegank/spice-gtk-darwin

spice-gtk: fix build on darwin

pkgs/development/libraries/spice-gtk/default.nix

···
     "-Dpolkit=disabled"
   ] ++ lib.optionals (!stdenv.isLinux) [
     "-Dlibcap-ng=disabled"
+    "-Degl=disabled"
   ] ++ lib.optionals stdenv.hostPlatform.isMusl [
     "-Dcoroutine=gthread" # Fixes "Function missing:makecontext"
   ];