Add GDK-specific symbols to clutter.symbols
Add GDK-specific symbols to clutter.symbols

A GDK backend for clutter was added in commits 610a9c17
(Add A new GDK backend) and f14cbf5b (gdk: Allow disabling event retrieval)

These are not included in the Win32 builds for the moment as GDK3 is
quite unstable on Windows at this time

kerrickstaley/clutter-vala,jigpu/clutter,GNOME/clutter,GNOME/clutter,djdeath/clutter,djdeath/clutter-android,collects/clutter,heysion/clutter-clone,heysion/clutter-clone,djdeath/clutter-android,djdeath/clutter-android,djdeath/clutter-android,collects/clutter,djdeath/clutter-android,djdeath/clutter,djdeath/clutter,djdeath/clutter,djdeath/clutter-multithreaded,GNOME/clutter,ebassi/clutter,djdeath/clutter-multithreaded,heysion/clutter-clone,jigpu/clutter,ebassi/clutter,collects/clutter,heysion/clutter-clone,ebassi/clutter,heysion/clutter-clone,kerrickstaley/clutter-vala,Distrotech/clutter,Distrotech/clutter,jigpu/clutter,GNOME/clutter,jigpu/clutter,collects/clutter,collects/clutter,djdeath/clutter,ebassi/clutter,ebassi/clutter,djdeath/clutter-multithreaded,kerrickstaley/clutter-vala,jigpu/clutter,GNOME/clutter,jigpu/clutter,Distrotech/clutter,kerrickstaley/clutter-vala,Distrotech/clutter,Distrotech/clutter,djdeath/clutter-multithreaded,Distrotech/clutter,djdeath/clutter