This keymap is meant to be used with a Bépo layout. It is designed to be somewhat similar to a TypeMatrix keyboard so that switching between one and the other is easy.
To build this on Windows, under Cygwin, provided that you have installed the Arduino environment and Teensy loaded in the default path, you can do:
PATH=/cygdrive/c/Program\ Files\ \(x86\)/Arduino/hardware/tools/avr/bin:$PATH
make ergodox_ez:bepo_tm_style:all
See https://github.com/tmk/tmk_keyboard#magic-commands for command that can help debug, together with the hid_listen tool.