Fix a bug in Makefile

Makefile

@@ -4,8 +4,8 @@ LIBS = -lboost_filesystem
 
 OBJS = $(patsubst %.c, %.o, $(wildcard *.c)) \
 	   $(patsubst %.cc, %.o, $(wildcard *.cc))
-C_DEPS = $(patsubst %.o, %.dep, $(wildcard *.c))
-CXX_DEPS = $(patsubst %.o, %.depxx, $(wildcard *.cc))
+C_DEPS = $(patsubst %.c, %.dep, $(wildcard *.c))
+CXX_DEPS = $(patsubst %.cc, %.depxx, $(wildcard *.cc))
 
 tx01_data : $(OBJS)
 	$(CXX) $(LDFLAGS) -o $@ $^ $(LIBS)
@@ -24,4 +24,4 @@ sinclude $(DEPS)
 
 .PHONY : clean
 clean:
-	echo $(RM) -f tx01_data $(OBJS) $(C_DEPS) $(CXX_DEPS)
+	$(RM) tx01_data $(OBJS) $(C_DEPS) $(CXX_DEPS)