Add test for issue-68841

Author: JohnTitor

src/test/ui/mir/issue-68841.rs

@@ -0,0 +1,15 @@
+// compile-flags: -Z mir-opt-level=2
+// edition:2018
+// build-pass
+
+#![feature(async_closure)]
+
+use std::future::Future;
+
+fn async_closure() -> impl Future<Output = u8> {
+    (async move || -> u8 { 42 })()
+}
+
+fn main() {
+    let _fut = async_closure();
+}