build: Dist every backend file
build: Dist every backend file

All backend files should be present in the tarball generated by `make
dist`, to allow building Clutter on different platforms.

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