Auto merge of rust-lang#104527 - ferrocene:pa-more-licenses, r=pnkfelix

Add more license annotations

This PR updates the `.reuse/dep5` file to include more accurate licensing data for everything in the repository (*excluding* submodules and dependencies). Some decisions were made in this PR:

* The standard copyright attribution for files maintained by us is "The Rust Project Developers (see https://thanks.rust-lang.org)", to avoid having to maintain an in-tree `AUTHORS` file.
* For files that have specific licensing terms, we added the terms to the `.reuse/dep5` rather than adding SPDX comments in the files themselves.
* REUSE picks up any comment/text line with `Copyright` on it, so I had to sprinkle around `REUSE-IgnoreStart` and `REUSE-IgnoreEnd` comments.

The rendered `COPYRIGHT` file is available at https://gist.github.com/pietroalbini/efb81103f69596d39758114f3f6a8688.

r? `@pnkfelix`

Author: bors

example/alloc_system.rs

@@ -1,12 +1,6 @@
-// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
+// SPDX-License-Identifier: MIT OR Apache-2.0
+// SPDX-FileCopyrightText: The Rust Project Developers (see https://thanks.rust-lang.org)
+
 #![no_std]
 
 pub struct System;