see build.log Reproducible: Always
Created attachment 420238 [details] build log
Created attachment 420240 [details] emerge --info
I think I had the same problem, again it seems like gcc 5 stuff, try rebuilding qpdf and other deps.
the ebuild should update its own deps or some @rebuild option should check this. I'll let you know in a moment exactly which dep is causing the error.
qpdf was the only dep that needed to be rebuilt
https://www.gentoo.org/support/news-items/2015-10-22-gcc-5-new-c++11-abi.html