kde-misc/semantik depends on dev-qt/qtwebkit:4 which is ancient and will never see any security updates. If it's not possible to disable it and there's no upstream port available it might be time to remove this package.
commit fb59bc17029aa0bc06ee951258de745213648e96 Author: Michał Górny <mgorny@gentoo.org> AuthorDate: Sun Jul 30 09:10:47 2017 Commit: Michał Górny <mgorny@gentoo.org> CommitDate: Sun Jul 30 09:14:15 2017 kde-misc/semantik: Remove last-rited pkg, #620700