Auto generate source via make file

[agorrod]

I'm having trouble getting the source file auto-generation to be triggered by Make.

At the moment to build I'm running:

(cd dist && python gen_source.py) && make

Ideally I'd just be able to run make, and have it run the python command. Even more ideally it'd only run the python command if it noticed that one of src/faultinject.c.in, dist/functions.list or dist/gen_source.py had changed. My half hour of fiddling didn't lead me to a resolution so I'm opening an issue for now.