* gnu/packages/arcan.scm (arcan): Build all features.
[arguments]: Use #:configure-flags "-DBUILD_PRESET=everything" to build all
features, and "-DDISTR_TAG='Guix'" to tag the builds.
[synopsis]: Remove '(egl-dri)' since it indicates a specific feature.
Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>