The cogl-gles2-gears example will fail to build unless
--enable-cogl-gles2 is enabled in the configure script because it
depends on libcogl-gles2. This patch makes it only conditionally build
the example depending on the BUILD_COGL_GLES2 automake conditional.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
(cherry picked from commit 7f57e9c444b6353ac17e920ea4fc63ebe3cc29d3)