Get rid of warning about not being able to create an existing directory.
diff --git a/Makefile.pre.in b/Makefile.pre.in
index 0972411..7dfa738 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -475,7 +475,7 @@
 
 
 $(GRAMMAR_H) $(GRAMMAR_C): $(PGEN) $(GRAMMAR_INPUT)
-		-@ mkdir Include
+		-@$(INSTALL) -d Include
 		-$(PGEN) $(GRAMMAR_INPUT) $(GRAMMAR_H) $(GRAMMAR_C)
 
 $(PGEN):	$(PGENOBJS)