Kernel prepatch 4.20-rc5

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