When needing type annotations in local bindings, account for impl Trait and closures

Do not suggest nonsensical types when the type inference is failing on
`impl Trait` or anonymous closures.

src/test/ui/inference/cannot-infer-async.rs

@@ -0,0 +1,16 @@
+// edition:2018
+#![feature(async_await)]
+
+use std::io::Error;
+
+fn make_unit() -> Result<(), Error> { 
+    Ok(())
+}
+
+fn main() {
+    let fut = async {
+        make_unit()?; //~ ERROR type annotations needed
+        
+        Ok(())
+    };
+}