FN in boxed_local lint

[flip1995]

This FN was introduced by the rustup #4628. To fix this major changes to the lint are probably necessary (#4628 (comment)).

A test for this FN already exists here:

rust-clippy/tests/ui/escape_analysis.rs

Lines 170 to 174 in e2393b0

	fn closure_borrow(x: Box<A>) {
	let _ = || {
	borrow(&x);
	};
	}

Originally posted by @flip1995 in #4628