Per comment in: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=82733f406991c0f76109a88e63a4fc59e929b716 it seems it should reintroduce the CPU patch... but the options are still missing and I cannot see the patch neither in genpatches-5.1-2.base.tar.xz or genpatches-5.1-2.extras.tar.xz Thanks!
Can be worked around by editing the ebuild if you're impatient; K_WANT_GENPATCHES="base extras" -> K_WANT_GENPATCHES="base extras experimental" Then 'ebuild gentoo-sources-5.1.2.ebuild digest'
I missed the experimental use flag. It's in 5.1.2, now. Should be on the mirrors in a few hours. I plan on removing 5.1.0 and 5.1.1 soonish. But you can add it manually if needed in that specific version.
Thanks!