The latest version in portage is over an year old, the latest version as of today is 0.1.141-1.
Created attachment 504630 [details, diff] diff copy virtio-win-0.1.126.ebuild to you local portage overlay as virtio-win-0.1.141.ebuild, apply the patch attached, run repoman manifest and thats it.
https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=55619b4fa1bc94e38f92c76612ddd9b00e09ef66 thanks for the report.