gtk3: Fix for missing symbols (again)
Was removed again in f9a62dbace5b0f7924f59ade45c750479a6ab0ab, but it
was still needed after all, see https://github.com/NixOS/nixpkgs/issues/55692#issuecomment-469058386
(cherry picked from commit e0cc49c21948eb48935b1254602e1c2eb1d1d8ce)