Added libstack files to Makefile

Makefile

@@ -1,5 +1,5 @@
 EXEC_FILE=main
-TARGETS=$(EXEC_FILE).o message.o user.o message_helpers.o file_helpers.o
+TARGETS=$(EXEC_FILE).o message.o user.o message_helpers.o file_helpers.o stack.o
 CFLAGS=
 
 
@@ -14,6 +14,7 @@ message.o: message.c
 user.o: user.c
 message_helpers.o: message_helpers.c
 file_helpers.o: file_helpers.c
+stack.o: stack.c
 $(TARGETS):
 	gcc $(CFLAGS) -c -o $@ $^