CLUTTER_EGL_BACKEND is used to define a special EGL native backend to
use and was introduced for the CEX100 EGL backend. Unfortunately
CLUTTER_EGL_BACKEND was defined to "cex100" for eglnative, which is
obviously wrong.

The paches defines the right values for CLUTTER_EGL_BACKEND for the
eglnative and cex100 flavours.