recover from for-else and while-else

tests/ui/while/while-else-let-else-err.rs

@@ -0,0 +1,8 @@
+fn main() {
+    let _ = while false {
+        //~^ NOTE `else` is attached to this loop
+    } else {
+        //~^ ERROR `while...else` loops are not supported
+        //~| NOTE consider moving this `else` clause to a separate `if` statement and use a `bool` variable to control if it should run
+    };
+}