Install this version:
emerge -a =virtual/linux-sources-99
If this version is masked, you can unmask it using the autounmask tool or standard emerge options:
autounmask =virtual/linux-sources-99
Or alternatively:
emerge --autounmask-write -a =virtual/linux-sources-99
# Copyright 1999-2020 Gentoo Foundation # Distributed under the terms of the GNU General Public License v2 EAPI=5 DESCRIPTION="Dummy virtual for Linux kernel sources as dependency placeholder" HOMEPAGE="" SRC_URI="" LICENSE="" SLOT="0" KEYWORDS="amd64 arm x86" IUSE="" DEPEND="" RDEPEND=""