Created attachment 529508 [details] build.log When specifying MAKEOPTS="-j4" the build fails when using moc (see attached log). With MAKEOPTS="-j1" the merge fails only when linking. I will file another bug for that. I've tried it with cmake-3.11.1.
Thank you for the report. Perhaps we can work with this information already, but please provide also the emerge info just in case as described on https://wiki.gentoo.org/wiki/Attach_the_logs_to_the_bug_ticket so that we have all at hand.
Created attachment 529642 [details] emerge--info.gz Sorry, here is it.
The bug is gone now. I don't know why. Maybe this has to do with #654686, althought I'm not able to make a connection. Thank you anyway.