This package fails to build on an unstable system. Attached relevant logs and emerge --info
Created attachment 768137 [details] emerge_info emerge --info
Created attachment 768138 [details] ipopt-3.14.4:20220329-090748.log build log
Should be fixed. https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=7146c3276dcc8eb2cafe22fe7060c63d6088673f