We don't build xmkmf so any values returned from it are going to be wrong.
Using any paths in /usr/ for x headers/libs is a bad idea when cross compiling.
This patch removes them to stop any confusion.

RP - 20071115

Index: autoconf-2.61/lib/autoconf/libs.m4
===================================================================
--- autoconf-2.61.orig/lib/autoconf/libs.m4	2006-10-15 01:12:02.000000000 +0000
+++ autoconf-2.61/lib/autoconf/libs.m4	2007-11-15 12:09:59.000000000 +0000
@@ -180,53 +180,6 @@
 # --------------------- #
 
 
-# _AC_PATH_X_XMKMF
-# ----------------
-# Internal subroutine of _AC_PATH_X.
-# Set ac_x_includes and/or ac_x_libraries.
-m4_define([_AC_PATH_X_XMKMF],
-[AC_ARG_VAR(XMKMF, [Path to xmkmf, Makefile generator for X Window System])dnl
-rm -f -r conftest.dir
-if mkdir conftest.dir; then
-  cd conftest.dir
-  cat >Imakefile <<'_ACEOF'
-incroot:
-	@echo incroot='${INCROOT}'
-usrlibdir:
-	@echo usrlibdir='${USRLIBDIR}'
-libdir:
-	@echo libdir='${LIBDIR}'
-_ACEOF
-  if (export CC; ${XMKMF-xmkmf}) >/dev/null 2>/dev/null && test -f Makefile; then
-    # GNU make sometimes prints "make[1]: Entering...", which would confuse us.
-    for ac_var in incroot usrlibdir libdir; do
-      eval "ac_im_$ac_var=\`\${MAKE-make} $ac_var 2>/dev/null | sed -n 's/^$ac_var=//p'\`"
-    done
-    # Open Windows xmkmf reportedly sets LIBDIR instead of USRLIBDIR.
-    for ac_extension in a so sl; do
-      if test ! -f "$ac_im_usrlibdir/libX11.$ac_extension" &&
-	 test -f "$ac_im_libdir/libX11.$ac_extension"; then
-	ac_im_usrlibdir=$ac_im_libdir; break
-      fi
-    done
-    # Screen out bogus values from the imake configuration.  They are
-    # bogus both because they are the default anyway, and because
-    # using them would break gcc on systems where it needs fixed includes.
-    case $ac_im_incroot in
-	/usr/include) ac_x_includes= ;;
-	*) test -f "$ac_im_incroot/X11/Xos.h" && ac_x_includes=$ac_im_incroot;;
-    esac
-    case $ac_im_usrlibdir in
-	/usr/lib | /lib) ;;
-	*) test -d "$ac_im_usrlibdir" && ac_x_libraries=$ac_im_usrlibdir ;;
-    esac
-  fi
-  cd ..
-  rm -f -r conftest.dir
-fi
-])# _AC_PATH_X_XMKMF
-
-
 # _AC_PATH_X_DIRECT
 # -----------------
 # Internal subroutine of _AC_PATH_X.
@@ -234,40 +187,7 @@
 m4_define([_AC_PATH_X_DIRECT],
 [# Standard set of common directories for X headers.
 # Check X11 before X11Rn because it is often a symlink to the current release.
-ac_x_header_dirs='
-/usr/X11/include
-/usr/X11R6/include
-/usr/X11R5/include
-/usr/X11R4/include
-
-/usr/include/X11
-/usr/include/X11R6
-/usr/include/X11R5
-/usr/include/X11R4
-
-/usr/local/X11/include
-/usr/local/X11R6/include
-/usr/local/X11R5/include
-/usr/local/X11R4/include
-
-/usr/local/include/X11
-/usr/local/include/X11R6
-/usr/local/include/X11R5
-/usr/local/include/X11R4
-
-/usr/X386/include
-/usr/x386/include
-/usr/XFree86/include/X11
-
-/usr/include
-/usr/local/include
-/usr/unsupported/include
-/usr/athena/include
-/usr/local/x11r5/include
-/usr/lpp/Xamples/include
-
-/usr/openwin/include
-/usr/openwin/share/include'
+ac_x_header_dirs=''
 
 if test "$ac_x_includes" = no; then
   # Guess where to find include files, by looking for Xlib.h.
@@ -316,7 +236,6 @@
 [AC_CACHE_VAL(ac_cv_have_x,
 [# One or both of the vars are not set, and there is no cached value.
 ac_x_includes=no ac_x_libraries=no
-_AC_PATH_X_XMKMF
 _AC_PATH_X_DIRECT
 case $ac_x_includes,$ac_x_libraries in #(
   no,* | *,no | *\'*)