Auto-detect X11 path from the following list:

/usr/X11R6	(What MIT does by default)
/usr/X11	(Usually a symlink to the current X11R*)
/usr/X		(Non-MIT implementations use this - eg: Solaris)
/usr		(Ubuntu 5.10 - <censored>)

src/conio/Common.gmake

@@ -46,6 +46,8 @@ ifdef WITH_SDL
  endif
 endif
 
+X_PATH ?=      $(shell if [ -f /usr/X11R6/include/X11/Xlib.h ]; then echo /usr/X11R6 ; elif [ -f /usr/X11/include/X11/Xlib.h ] ; then echo /usr/X11 ; elif [ -f /usr/X/include/X11/Xlib.h ] ; then echo /usr/X ; elif [ -f /usr/include/X11/Xlib.h ] ; then echo /usr ; else echo 0 ; fi)
+
 ifeq ($(os),sunos)
  X_PATH	?=	/usr/X
 else