stty/flags: Add delayed suspend (dsusp) support

It's only supported by BSD, aix and solaris, but still available in nix

Author: 3v1n0

src/uu/stty/src/flags.rs

@@ -357,6 +357,18 @@ pub const CONTROL_CHARS: &[(&str, S)] = &[
     ("stop", S::VSTOP),
     // Sends a suspend signal (SIGTSTP).
     ("susp", S::VSUSP),
+    #[cfg(any(
+        target_os = "freebsd",
+        target_os = "dragonfly",
+        target_os = "ios",
+        target_os = "macos",
+        target_os = "netbsd",
+        target_os = "openbsd",
+        target_os = "aix",
+        target_os = "solaris"
+    ))]
+    // Sends a delayed suspend signal (SIGTSTP).
+    ("dsusp", S::VDSUSP),
     // Reprints the current line.
     ("rprnt", S::VREPRINT),
     // Deletes the last word typed.