(TAGS): Put DEPFILES back and add as a dependency.

gdb/Makefile.in

@@ -1227,12 +1227,12 @@ gdb1$(EXEEXT): gdb$(EXEEXT)
 # TAGS depends on all the files that go into it so you can rebuild TAGS
 # with `make TAGS' and not have to say `rm TAGS' first.
 
-TAGS: $(TAGFILES_NO_SRCDIR) $(TAGFILES_WITH_SRCDIR)
+TAGS: $(DEPFILES) $(TAGFILES_NO_SRCDIR) $(TAGFILES_WITH_SRCDIR)
 	@echo Making TAGS
 	@etags $(srcdir)/$(DEPRECATED_TM_FILE) \
 	  $(srcdir)/$(XM_FILE) \
 	  $(srcdir)/$(NAT_FILE) \
-	`(for i in $(TAGFILES_NO_SRCDIR); do \
+	`(for i in $(DEPFILES) $(TAGFILES_NO_SRCDIR); do \
 		echo $(srcdir)/$$i ; \
 	done ; for i in $(TAGFILES_WITH_SRCDIR); do \
 		echo $$i ; \