Purpose: adding $(CPPFLAGS) as argument to CC, for hardening build.
Author: Zhou Mo
Forward: keep it downstream -- Debian specific.
--- a/Makefile
+++ b/Makefile
@@ -13,9 +13,9 @@
 MANDIR = $(PREFIX)/share/man/man1
 
 $(OBJ) : progress.o sizes.o hlist.o
-	$(CC) -Wall $^ -o $@ $(LDFLAGS)
+	$(CC) $(CPPFLAGS) -Wall $^ -o $@ $(LDFLAGS)
 %.o : %.c
-	$(CC) $(CFLAGS) -c $^
+	$(CC) $(CPPFLAGS) $(CFLAGS) -c $^
 clean :
 	rm -f *.o $(OBJ)
 install : $(OBJ)
