[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/debug/ui/debug_window.cc

@@ -309,7 +309,7 @@ void DebugWindow::DrawToolbar() {
       case cpu::ThreadDebugInfo::State::kAlive:
       case cpu::ThreadDebugInfo::State::kExited:
       case cpu::ThreadDebugInfo::State::kWaiting:
-        if (thread_info->thread_handle == NULL || thread_info->thread == NULL) {
+        if (!thread_info->thread_handle || thread_info->thread == nullptr) {
           thread_combo.Append("(invalid)");
         } else {
           thread_combo.Append(thread_info->thread->thread_name());