dri3: Add DRI3 extension

Adds DRM compatible fences using futexes.
Uses FD passing to get pixmaps from DRM applications.

Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>

include/extinit.h

@@ -176,4 +176,9 @@ extern void XvExtensionInit(void);
 extern void XvMCExtensionInit(void);
 #endif
 
+#if defined(DRI3)
+#include <X11/extensions/dri3proto.h>
+extern void dri3_extension_init(void);
+#endif
+
 #endif