Created attachment 456032 [details, diff] Patch fixing usex I tried emerging sci-mathematics/z3 and build failed with x86_64-pc-linux-gnu-g++: error: no: No such file or directory because usex outputs "no" by default if no false output is specified (https://devmanual.gentoo.org/eclass-reference/ebuild/index.html). The attached patch fixed this issue for me. I see z3-9999 should also be patched accordingly.
Created attachment 456034 [details] Failed build log
I added z3 with the fixes, thanks, to portage. As z3 is required by sci-mathematics/isabelle. commit e1bee0588417636345663574e7c1ef127abbebe6 Author: Mark Wright <gienah@gentoo.org> Date: Mon Jan 2 11:18:51 2017 +1100 sci-mathematics/z3: Thanks to Yichao Zhou, jlec and slyfox for development on the z3 ebuilds. Thanks to David E. Narv?ez for reporting and patching. Gentoo-bug: 602498, 602600