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

[Paul Gofman (＠gofman)]

This is a preparation for supporting more xstate features in the contexts.

The remaining parts are:
- support arbitrary xstate in usr1_handler();
- support arbitrary xstate in the server contexts (probably transferring only the present part);
- support arbitrary xstate in context manipulation functions;
- enabling more xstates in system.c and in user shared data.