http://mldonkey.sourceforge.net/forums/viewtopic.php?p=31821#31821
--- Makefile.orig	2011-08-08 00:11:57.000000000 -0500
+++ Makefile	2012-01-18 20:59:40.000000000 -0600
@@ -5447,7 +5447,7 @@
 	$(OCAMLC) $(DEVFLAGS) $(INCLUDES) -c $<
 
 .mlcpp.ml:
-	@cpp -P $< $(FIX_BROKEN_CPP) > $@
+	@$(CPP) -x c -P $< $(FIX_BROKEN_CPP) > $@
 
 %.ml: %.mlp $(BITSTRING)/pa_bitstring.cmo
 	$(CAMLP4OF) build/bitstring.cma $(BITSTRING)/bitstring_persistent.cmo $(BITSTRING)/pa_bitstring.cmo -impl $< -o $@
