If you want to flash system on builtin flash
To cross-compile C++ code on your PC for Luckfox you need to download official SDK:
git clone https://github.com/LuckfoxTECH/luckfox-pico
export GCC_COMPILER=<ABSOLUTE_PATH>/luckfox-pico/tools/linux/toolchain/arm-rockchip830-linux-uclibcgnueabihf/bin/arm-rockchip830-linux-uclibcgnueabihf
Replace <ABSOULTE_PATH>
with yours