--- makefile.orig	2014-02-19 11:28:02.790529666 +0100
+++ makefile	2014-02-19 11:28:28.407549409 +0100
@@ -17,12 +17,12 @@
 OPTFLAGS = -g
 #DFLAGS = -DBETTERHASH  -DSMV_SIGNALS -DOTHER_SIMP -DSERGEYDEBUG
 DFLAGS = -DBETTERHASH -DSMV_SIGNALS -DOTHER_SIMP
-CFLAGS =  $(OPTFLAGS) -I. $(DFLAGS) $(REORDER) $(TIMING) $(VERFLAG)
+CFLAGS +=  $(OPTFLAGS) -I. $(DFLAGS) $(REORDER) $(TIMING) $(VERFLAG)
 LIB = -lm $(MACHLIB)
 OBJ = grammar.o input.o init.o main.o assoc.o bdd.o  hash.o node.o storage.o \
 	string.o symbols.o
 EXEC = smv
-CC = gcc
+CC ?= gcc
 M4 = m4
 #M4 = gm4