Kernel prepatch 6.4-rc1

The one feature that didn't make it was the x86 shadow stack code. That side was probably a bit unlucky, in that it came in as I was looking at x86 issues anyway, and so I looked at it quite a bit, and had enough reservations that I asked for a couple of fairly big re-organizations.

This is just one more setback in the long-running shadow-stack story; see this article for some background.

In the end, 13,044 non-merge changesets were pulled during this merge window.