Use depend file for header build dependencies

.gitignore

@@ -1,3 +1,4 @@
+.depend
 config.h
 *.o
 sxiv

Makefile

@@ -1,4 +1,4 @@
-VERSION = git-20141001
+VERSION = git-20141024
 
 PREFIX    = /usr/local
 MANPREFIX = $(PREFIX)/share/man
@@ -16,6 +16,14 @@ all: sxiv
 
 $(OBJ): Makefile config.h
 
+depend: .depend
+
+.depend: $(SRC)
+	rm -f ./.depend
+	$(CC) $(CFLAGS) -MM $^ >./.depend
+
+include .depend
+
 .c.o:
 	$(CC) $(CFLAGS) $(CPPFLAGS) -DVERSION=\"$(VERSION)\" -c -o $@ $<