message: avoid importing __sys_malloc during cargo tests
diff: @@ -28,6 +28,7 @@ pub use self::spinlock::*;
  pub use self::system::*;
  pub use self::tasks::*;
  pub use self::timer::*;
  +#[cfg(not(test))]
  use crate::{__sys_free, __sys_malloc, __sys_realloc};
  use environment;
  #[cfg(feature = "newlib")]
  