Excessive dependencies for the last-updated target

[ghost]

Bug from Marshall Miller:

I believe the repos/my--repos/last-updated target has excessive dependencies. It appropriately depends on the pkglist. and pkglist.blacklist files. The dependencies on Makefile, CONFIG_BUILD, and CONFIG_REPOS seem inappropriate. I believe that if someone has modified these files in a major way, they should be aware that this is a major change, and they should run make bare before attempting subsequent builds.

If we want to prevent someone from shooting themselves in the foot, we could add a file/target whose purpose is to warn the user if they have modified one of these critical files and have not run make bare (or maybe make clean). One way I think this could be implemented is like so:

$(info $(shell cat build_message))

...

build_message: Makefile CONFIG_BUILD CONFIG_REPOS
@echo "WARNING: a critical file was modified; run make clean if critical changes were made" | tee build_message

clean:
...
@echo -n "" > build_message