Add support for the Qt 5 application and UI framework

Packages describing “qt5” as local USE flag

Package “qt5” Flag Description
media-libs/OpenImageIO Build iv with Qt5
media-libs/OpenShadingLanguage Build the osltoy binary
net-p2p/bitcoin-core Build and install Bitcoin-Qt GUI
games-simulation/flightgear Build Qt5 launcher application
media-gfx/renderdoc Build and install the qrenderdoc GUI
media-libs/osl Build the osltoy binary
media-video/guvcview Build with Qt5 interface instead Gtk+
dev-libs/quazip Build with Qt5 support
media-libs/openimageio Build iv with Qt5
dev-python/pyudev Install PyQt5 bindings

All packages providing a “qt5” USE flag (87)