Added test for spurious cannot borrow immutable item error with a closure

Author: davidtwco

src/test/run-pass/issue-16671.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+//compile-flags: -Z borrowck=compare -Z emit-end-regions
+
 #![deny(warnings)]
 
 fn foo<F: FnOnce()>(_f: F) { }