error[E0463]: can't find crate for `std`
  |
  = note: the `thumbv6m-none-eabi` target may not support the standard library
  = note: `std` is required by `autocfg_3440057aadc8fa69_0` because it does not declare `#![no_std]`

error: cannot resolve a prelude import

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0463`.