Merge branch 'cyclic-unload' into 'master'

Fix dynamic linker hitting unwrap

See merge request redox-os/relibc!1067

src/ld_so/linker.rs

@@ -561,12 +561,11 @@ impl Linker {
 
             let _ = self.objects.remove(&obj.id).unwrap();
             for dep in obj.dependencies() {
-                self.unload(ObjectHandle::new(
-                    self.objects
-                        .get(self.name_to_object_id_map.get(*dep).unwrap())
-                        .unwrap()
-                        .clone(),
-                ));
+                if let Some(name) = self.name_to_object_id_map.get(*dep) {
+                    if let Some(object_name) = self.objects.get(name) {
+                        self.unload(ObjectHandle::new(object_name.clone()));
+                    }
+                }
             }
             self.name_to_object_id_map.remove(&obj.name);
             assert!(Arc::strong_count(&obj) == 1);