Can't find gtk.h. Upstream patch fixes this for me: http://git.clutter-project.org/clutter-gtk/commit/?h=clutter-gtk-0.10&id=4de105a2bbd201c8e60f3e8777794a4cd532afdc
Could you please provide a full build.log and emerge --info.
Created attachment 258565 [details] build.log
Created attachment 258567 [details] emerge --info
Index: ChangeLog + 04 Jan 2011; Gilles Dartiguelongue <eva@gentoo.org> + -clutter-gtk-0.10.4.ebuild, -clutter-gtk-0.10.6.ebuild, + clutter-gtk-0.10.8.ebuild, + +files/clutter-gtk-0.10.8-fix-introspection-build.patch: + Fix build with USE=introspection, bug #350061. Clean up old revisions. Thanks for reporting.