Hi @AlexRusuf
Welcome to the FreeRTOS Community Forums !
It seems stdio.h might be missing in this version of arm-none-eabi-gcc . I am able to build the demo using this version
arm-none-eabi-gcc --version
arm-none-eabi-gcc (15:9-2019-q4-0ubuntu1) 9.2.1 20191025 (release) [ARM/arm-9-branch revision 277599]
Copyright (C) 2019 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
You can try installing libnewlib-arm-none-eabi to see if that fixes the issue.