[build] Clean up the makefile
[build] Clean up the makefile

Split out the files into their own variables to clean up the
Makefile template; also use top_srcdir with the header files
instead of top_builddir.

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