Looks like upstream is at 1.18.1 whereas portage latest is 1.18.0. I've copied over the ebuild and is compiles/works fine after removing the sandbox patch (which doesn't apply). See: https://github.com/mrpdaemon/gentoo-overlay/blob/master/x11-plugins/pidgin-sipe/pidgin-sipe-1.18.1.ebuild
+*pidgin-sipe-1.18.1 (10 May 2014) + + 10 May 2014; Ian Whyman <thev00d00@gentoo.org> +pidgin-sipe-1.18.1.ebuild, + -pidgin-sipe-1.17.3.ebuild: + Version bump, thanks to Mark R. Pariente for the reminder in #509942 + Thanks for reporting Mark.