[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/apu/audio_media_player.cc

@@ -13,8 +13,6 @@
 #include "xenia/apu/xma_context.h"
 #include "xenia/base/logging.h"
 
-#include <XAudio2.h>
-
 extern "C" {
 #if XE_COMPILER_MSVC
 #pragma warning(push)