Switched to profile 17.0 and followed all instructions according to news item "New 17.0 profiles in the Gentoo repository". During world rebuild, virtualbox fails to build. Presumably related to Bug 640910 (dev-util/kbuild).
Created attachment 509788 [details] Output of 'emerge --info =app-emulation/virtualbox-5.1.26::gentoo' Output of: # emerge --info '=app-emulation/virtualbox-5.1.26::gentoo'
Created attachment 509790 [details] Build log
Should be no longer an issue with virtualbox-5.1.32