Please enable glib in x11-libs/qt-core-4.4.2 via use defaults. x11-libs/qt-gui-4.4.2-r2 has IUSE="+glib" and in case glib is enabled it needs qt-core built with USE="glib". Additionally one could add a use-dependency, but that required EAPI=2.
Fixed in CVS. We will eapi2-ify the Qt ebuilds on next release, as this needs an eclass update.