Make x11 optional
Created by: kbrenneman
This lets you build libglvnd with EGL (but not GLX) without the X11 packages. Outside of GLX, the only thing that actually uses any of the X11 headers is EGL's platform detection.
This adds a new configure option, --disable-x11. It disables GLX (as per the --disable-glx option), and #ifdef's out the X11 support in EGL. You could still use X11 in EGL with eglGetPlatformDisplay, but eglGetDisplay wouldn't be able to recognize an Xlib display.