Making ‘make clean’ ask for confirmation

I’m not familiar with cmake, but for gnu make, one possible hack would be:

clean: check_clean

check_clean:
    @echo -n "Are you sure? [y/N] " && read ans && [ $${ans:-N} = y ]

.PHONY: clean check_clean

If check_clean fails (user does not type in y), then make will exit with an error before performing the clean.