Please remove the patch "zathura-9999-synctex.patch" from the app-text/zathura-9999 ebuild. It is obsolete since upstream commit b78be80d1 (Dec 21) and causes the build to fail.
commit 6d73c36e7dfa885c9bdaad4ab159eca8659c7429 Author: Michael Weber <xmw@gentoo.org> Date: Thu Jan 28 16:59:15 2016 +0100 app-text/zathura: drop synctex patch (bug 573162, thanks Luis Ressel). Package-Manager: portage-2.2.26