std: move stdio to `sys`

As per #117276, this moves the platform definitions of `Stdout` and friends into `sys`. This PR also unifies the UNIX and Hermit implementations and moves the `__rust_print_err` function needed by libunwind on SGX into the dedicated module for such helper functions.

1 files changed, 6 insertions, 0 deletions

diff --git a/library/std/src/sys/stdio/windows/tests.rs b/library/std/src/sys/stdio/windows/tests.rs
new file mode 100644
index 00000000000..1e53e0bee63
--- /dev/null
+++ b/library/std/src/sys/stdio/windows/tests.rs
@@ -0,0 +1,6 @@
+use super::utf16_to_utf8;
+
+#[test]
+fn zero_size_read() {
+    assert_eq!(utf16_to_utf8(&[], &mut []).unwrap(), 0);
+}