tomcat-8.x installed here. emerge world in stable arch emerges dev-java/tomcat-servlet-api-9 which is likely to be useless to the above. There might be some good reason for allowing its install I'm just not aware of. Reproducible: Always
I do not understand this report. Please open a new ticket with a clear summary and a complete description. We can help you on IRC #gentoo, how to write it properly. See also https://wiki.gentoo.org/wiki/Bugzilla/Guide