Fix Xcode 16.3 build (#9422)

* Fix build with Xcode 16.3

* Simplify OpenVDB patch, from 930c3acb8e (diff-bc3061cc2fe6c64a3d67c8350330bb3a530d01037faace6da27ad9a12aa03e29)

* Fix CGAL header under clang 19
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=281880

* Fix compile error due to removal of base template for `std::char_traits` in clang 19
https://releases.llvm.org/19.1.0/projects/libcxx/docs/ReleaseNotes.html#deprecations-and-removals

src/slic3r/GUI/GUI_App.cpp

@@ -4053,7 +4053,7 @@ void GUI_App::on_http_error(wxCommandEvent &evt)
         try {
         auto evt_str = evt.GetString();
         if (!evt_str.empty()) {
-            json j = json::parse(evt_str);
+            json j = json::parse(evt_str.utf8_string());
             if (j.contains("code")) {
                 if (!j["code"].is_null())
                     code = j["code"].get<int>();