I believe there is no way to generate dependency information with M4 as we do in CPP with -MD. Right?
After some searching I've seen that there have been some wishes for this feature in the past, but it has never been implemented. I've browsed a bit in the last version of the sources and I think it could be implemented within m4_push_file() in input.c. Do you see any problem with it?
Personally, for a quick and dirty solution I would just dump all 'title' values in a file and post-process it.