xsave is part of SSE2, not AVX, and it should ignore unsupported
requested features, so the patch should be fine as is on hardware
without AVX. xsave needs, however, to be enabled by OS, so we may need
a feature check if we want to support OSes without xsave enabled.

There was a real bug with that:
https://bugs.winehq.org/show_bug.cgi?id=50271.

Looking at the bug report, I think it was about missing AVX support, not missing XSAVE support, so it should be fine with my patches.

I would need to do testing to be sure, but I noticed that our feature detection looks suspicious. I would expect that we should do something like the attached patch (but if it's right, it would also need fixes in ntdll).

Jacek