The latest rewrite of the Makefile creates the hex-files for the target boards "CORE", "MINDEV", "W1209", and "C0135" by running a make.

If you want to build and flash just one target, e.g. W1209, instead run

make BOARD=W1209 flash

By the way, I also published a snapshot of the hex-files for the boards mentioned above in the files section. For first tests, e.g. with the STM8S003F3P6 "minimal development board", all you need is an ST-LINK V2 adapter, and a serial interface with "TTL" level.