<{dix,dmx}-config.h> to the source files.
change "foo.h" to <X11/foo.h> for core headers, e.g. X.h, Xpoll.h; change "foo.h", "extensions/foo.h" and "X11/foo.h" to <X11/extensions/foo.h> for extension headers, e.g. Xv.h; change "foo.[ch]" to <X11/Xtrans/foo.[ch]> for Xtrans files.