Another list to maintain by hand. We could split the variables declaring
the source files into private and public header in a separate Makefile
and then include it from both doc/reference/cogl/Makefile and
cogl/Makefile, but I'll leave this for the next person to look at the
documentation.
(cherry picked from commit f2daeb45fe118b848fbb2ad755d632d5699cd98b)
58680d3a4f
