[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/kernel/xam/xam_net.cc

@@ -722,7 +722,7 @@ dword_result_t NetDll_getsockopt_entry(dword_t caller, dword_t socket_handle,
     return -1;
   }
 
-  int native_len = *optlen;
+  uint32_t native_len = *optlen;
   X_STATUS status = socket->GetOption(level, optname, optval_ptr, &native_len);
   return XSUCCEEDED(status) ? 0 : -1;
 }