Re: [PATCH v2 0/3] MR4987: ntdll: Support generic xstate (part 1).

[Paul Gofman (＠gofman)]

v2:
 - use xstate_features_size, xstate_features_mask from thread_data in asm functions also on x64;
 - make sure thread_data()->xstate_features_size is always initialized before signal_start_thread();
 - don't rename xstate to xstate_hdr in syscall frame.