[All] Fixed multiple issues during build on Linux

- Added some fixes introduced by RodoMa92 in PR198

- Lack of AVX2 extension (should be done differently in the future)
- Disable deprecated-volatile warning
- Added missing override in posix EventInfo, ImGui notification class and XContent class
- Removed not used XAudio2.h include in XMP
- Fixed missing switch-case in XObject
- Added fugly template in native_list.h
- Fixed multiple smaller issues

src/xenia/ui/imgui_host_notification.h

@@ -32,7 +32,7 @@ class ImGuiHostNotification : public ImGuiNotification {
   const ImVec2 CalculateNotificationSize(ImVec2 text_size,
                                          float scale) override;
 
-  virtual void OnDraw(ImGuiIO& io) {}
+  virtual void OnDraw(ImGuiIO& io) override {}
 };
 
 class HostNotificationWindow final : ImGuiHostNotification {