multitask: properly detach when dropping JoinHandle

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>

Author: Keruspe

src/task/join_handle.rs

@@ -66,6 +66,15 @@ impl<T> JoinHandle<T> {
     }
 }
 
+#[cfg(not(target_os = "unknown"))]
+impl<T> Drop for JoinHandle<T> {
+    fn drop(&mut self) {
+        if let Some(handle) = self.handle.take() {
+            handle.detach();
+        }
+    }
+}
+
 impl<T> Future for JoinHandle<T> {
     type Output = T;