Kernel prepatch 4.20-rc5

The 4.20-rc5 kernel prepatch is out; amongother things, it contains the STIBP changes described in this article. Linus is also thinking aboutrelease timing: "So my current suggestion is that we plan on aChristmas release, everybody gets their pull requests for the next mergewindow done *before* the holidays, and then we see what happens. I think weall want to have a calm holiday season without either the stress of a mergewindow _or_ the stress of prepping for one."