Merge branch 'feature/toolchain_update' into 'master'

update toolchain version, rebuild newlib

- This MR updates the toolchain version used in the ESP-IDF
- Compiler version check and warning is added to project.mk
- Newlib is rebuilt to include wcsftime function
- libstdc++ build uses correct newlib headers (so we won't get undefined reference to `__impure_ptr` anymore)

See merge request !387