Adam Jackson authored Jul 01, 2021 and Povilas Kanapickas committed Sep 15, 2021

There's no real benefit to using GLX, and the other DDXes are using EGL
already, so let's converge on EGL so we can concentrate the fixes in one
place.

We go to some effort to avoid being the thing that requires libX11 here.
We prefer EGL_EXT_platform_xcb over _x11, and if forced to use the
latter we'll ask the dynamic linker for XGetXCBConnection and
XOpenDisplay rather than link against xlib stuff ourselves. Xephyr is
now a pure XCB application if it can be.

Reviewed-by: Emma Anholt <emma@anholt.net>