dev-util/ninja-ide depends on dev-qt/qtwebkit:4 which is ancient and will never see any security updates. If there's no upstream fix available, it might be time to remove this package.
It looks like a QT5 migration was started, but never completed. I think this project has mostly been abandoned by its developers. It was a neat IDE, but seems all but dead. It's probably time for removal.
commit 0618f2996ad74043e7f481fc76a056a616bfc0c8 Author: Michał Górny <mgorny@gentoo.org> AuthorDate: Mon Aug 14 09:25:26 2017 Commit: Michał Górny <mgorny@gentoo.org> CommitDate: Mon Aug 14 09:28:19 2017 dev-util/ninja-ide: Remove last-rited pkg, #620816 dev-util/ninja-ide/Manifest | 1 - .../ninja-ide/files/ninja-ide-2.3-python2_6.patch | 27 ------------- .../ninja-ide/files/ninja-ide-2.3-syntax.patch | 9 ----- dev-util/ninja-ide/metadata.xml | 28 ------------- dev-util/ninja-ide/ninja-ide-2.3.ebuild | 47 ---------------------- profiles/package.mask | 3 +- 6 files changed, 1 insertion(+), 114 deletions(-)