New Zathura version 0.3.3 Reproducible: Always the patch to the previous version is no longer necessary; requires dev-libs/girara-0.2.4; with that it compiles just fine here.
Created attachment 403604 [details] ebuild (this is the renamed ebuild for zathura 0.3.2 with the patch removed)
+*girara-0.2.4 (01 Jun 2015) + + 01 Jun 2015; Michael Weber <xmw@gentoo.org> +girara-0.2.4.ebuild: + Version bump (thanks Jan-Willem Liebezeit, bug 549874). +
+*zathura-0.3.3 (01 Jun 2015) + + 01 Jun 2015; Michael Weber <xmw@gentoo.org> +zathura-0.3.3.ebuild: + Version bump (thanks Jan-Willem Liebezeit, bug 549874). + +*zathura-pdf-mupdf-0.2.8 (01 Jun 2015) + + 01 Jun 2015; Michael Weber <xmw@gentoo.org> +zathura-pdf-mupdf-0.2.8.ebuild: + Version bump (thanks Jan-Willem Liebezeit, bug 549874). +
The dependencies probably need to be updated in the ebuild, zathura-0.3.3 fails here because of some hardcoded check for the GTK version.
The check is actually on girara-gtk, not gtk. It seems that portage did not enforce the requirement, that is in the ebuild, because I had -9999 installed, sorry for the noise. After "downgrading" girara to 0.2.4, zathura compiles.