Install this package:
emerge -a dev-util/lineageos-devel-meta
If the package is masked, you can unmask it using the autounmask tool or standard emerge options:
autounmask dev-util/lineageos-devel-meta
Or alternatively:
emerge --autounmask-write -a dev-util/lineageos-devel-meta
<pkgmetadata> <maintainer type="person"> <email>ykonotopov@gnome.org</email> <name>Yuri Konotopov</name> </maintainer> </pkgmetadata>