[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/base/threading_posix.cc

@@ -905,7 +905,7 @@ class PosixEvent : public PosixConditionHandle<Event> {
   ~PosixEvent() override = default;
   void Set() override { handle_.Signal(); }
   void Reset() override { handle_.Reset(); }
-  EventInfo Query() {
+  EventInfo Query() override {
     EventInfo result{};
     assert_always();
     return result;