Patch by Jason Bucata.
http://bugs.gentoo.org/84187

--- configure
+++ configure
@@ -5515,7 +5515,11 @@
 fi
 
 
-CFLAGS="-I $x_includes"
+if test "x$x_includes" != "x"; then
+  CFLAGS="-I $x_includes"
+else
+  CFLAGS=""
+fi
 LDFLAGS="-L/usr/local/lib -L$x_libraries -L$libdir"
 CXXFLAGS="$CFLAGS -Wall"