When building mutter 3.24 and trying to run it on Endless (which uses X11), I found the following runtime error that prevented the shell from running:

  Window manager error: Failed to get proc address for 'eglGetPlatformDisplayEXT'

While debugging, I found the error was happening due to GET_EGL_PROC_ADDR_REQUIRED (eglGetPlatformDisplayEXT) [1], which is called while initializing the backend. Talking to Jonas on IRC he mentioned that this should only be required on Wayland, so we probably can simply remove the _REQUIRED part (and the unused macro) and let the call to eglGetPlatformDisplay() error accordingly.

[1] https://github.com/GNOME/mutter/blob/master/src/backends/meta-egl.c#L777