Fuchsia apparently does not have DT_UNKNOWN.

Author: hkratz

library/std/src/sys/unix/fs.rs

@@ -1639,11 +1639,20 @@ mod remove_dir_impl {
         None
     }
 
+    #[cfg(target_os = "fuchsia")]
+    fn is_dir(ent: &DirEntry) -> Option<bool> {
+        match ent.entry.d_type {
+            libc::DT_DIR => Some(true),
+            _ => Some(false),
+        }
+    }
+
     #[cfg(not(any(
         target_os = "solaris",
         target_os = "illumos",
         target_os = "haiku",
-        target_os = "vxworks"
+        target_os = "vxworks",
+        target_os = "fuchsia"
     )))]
     fn is_dir(ent: &DirEntry) -> Option<bool> {
         match ent.entry.d_type {