Manual Debug for Unix ExitCode ExitStatus ExitStatusError

These structs have misleading names.  An ExitStatus[Error] is actually
a Unix wait status; an ExitCode is actually an exit status.

The Display impls are fixed, but the Debug impls are still misleading,
as reported in #74832.

Fix this by pretending that these internal structs are called
`unix_exit_status` and `unix_wait_status` as applicable.  (We can't
actually rename the structs because of the way that the cross-platform
machinery works: the names are cross-platform.)

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

library/std/src/sys/unix/process/process_common.rs

@@ -457,9 +457,15 @@ impl fmt::Debug for Command {
     }
 }
 
-#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+#[derive(PartialEq, Eq, Clone, Copy)]
 pub struct ExitCode(u8);
 
+impl fmt::Debug for ExitCode {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("unix_exit_status").field(&self.0).finish()
+    }
+}
+
 impl ExitCode {
     pub const SUCCESS: ExitCode = ExitCode(EXIT_SUCCESS as _);
     pub const FAILURE: ExitCode = ExitCode(EXIT_FAILURE as _);