Zephyr Workbench, a VSCode extension to manage Zephyr on STM32.
It enables users to easily create, develop, and debug Zephyr applications.
Main features:
Install host dependencies.
Import toolchain and SDK.
Create, configure, build and manage apps.
Debug STM32.
You can directly download it from the VSCode marketplace
For more details, visit the Zephyr Workbench
You are just missing the syscalls.c, see atached file
look at _write function which calls the _io_putchar function, this _write function is called by printf, puts, putc ...