Add test case for issue rust-lang#57017

Author: eholk

src/test/ui/generator/issue-57017.rs

@@ -0,0 +1,23 @@
+// check-pass
+#![feature(generators, negative_impls)]
+
+struct Client;
+
+impl !Sync for Client {}
+
+fn status(_client_status: &Client) -> i16 {
+    200
+}
+
+fn assert_send<T: Send>(_thing: T) {}
+
+// This is the same bug as issue 57017, but using yield instead of await
+fn main() {
+    let client = Client;
+    let g = move || {
+        match status(&client) {
+            _status => yield,
+        }
+    };
+    assert_send(g);
+}