If you look at the makefiles, they have lots of manually written dependencies. As an example, src/mame/mame.mak ends with dozens of lines that look like this:
These seem to be different than the depend target which is written to depend_ume.mak. Maybe these are remnants and not used?
But, more importantly, with Meson there is no "make depend" step, the dependency info db is created and updated automatically.