message: Use the ErrorCode enum directly
diff: #![no_std]
  use libtock_low_level_debug::{AlertCode, LowLevelDebug};
  -use libtock_platform::Syscalls;
  +use libtock_platform::{ErrorCode, Syscalls};
  use libtock_runtime::TockSyscalls;
  #[panic_handler]
  @@ -10,5 +10,5 @@ fn panic_handler(_info: &core::panic::PanicInfo) -> ! {
  LowLevelDebug::<TockSyscalls>::print_alert_code(AlertCode::Panic);
  // Exit with a non-zero exit code to indicate failure.
  - TockSyscalls::exit_terminate(1);
  + TockSyscalls::exit_terminate(ErrorCode::Fail as u32);
  }
  