Expose legacy stdio functions

rustsbi/src/lib.rs

@@ -151,3 +151,5 @@ pub use privileged::enter_privileged;
 pub use reset::{init_reset, Reset};
 pub use timer::{init_timer, Timer};
 pub use rfence::{init_rfence as init_remote_fence, Rfence as Fence};
+#[doc(hidden)]
+pub use legacy_stdio::{legacy_stdio_getchar, legacy_stdio_putchar};