Because the derived versions are good enough.

Currently it creates an `Option` and then does `map`/`unwrap_or` and
`map_or_else` on it, which is hard to read.

This commit simplifies things by moving more code into the two arms of
the if/else.

There are three very similar blocks in this function.

docs(std): clarify remove_dir_all errors

When using `remove_dir_all`, I assumed that the function was idempotent and that I could always call it to remove a directory if it existed. That's not the case and it bit me in production, so I figured I'd submit this to clarify the docs.

Correct `std::prelude` comment

(Read the changed file first for context.)

First, `alloc` has no prelude.

Second, the docs for `v1` don't matter since the [prelude module] already has all the doc links. The `rust_2021` module for instance also doesnt have a convenient doc page. However as I understand glob imports still cant be used because the items dont have the same stabilisation versions.

[prelude module]: https://doc.rust-lang.org/std/prelude/index.html

Change memory ordering in System wrapper example

Currently, the `SeqCst` ordering is used, which seems unnecessary:
+ Even `Relaxed` ordering guarantees that all updates are atomic and are executed in total order
+ User code only reads atomic for monitoring purposes, no "happens-before" relationships with actual allocations and deallocations are needed for this

If argumentation above is correct, I propose changing ordering to `Relaxed` to clarify that no synchronization is required here, and improve performance (if somebody copy-pastes this example into their code).

…cleanups, r=lcnr

More `Typefoldable`/`TypeVisitable` cleanups

r? ``@lcnr``

…=compiler-errors

compiletest: emit assembly-output header in error

Improve the error message.

…rt, r=wesleywiser

compiletest: add bpf-linker assembly support

…unsound-issues, r=jackh726

Add `known-bug` tests for 4 unsound issues

This PR adds `known-bug` tests for 4 unsound issues as part of rust-lang#105107
- rust-lang#40582
- rust-lang#49682
- rust-lang#74629
- rust-lang#105782

…cjgillot

`DepGraph` cleanups

r? `@cjgillot`

Remove invalid value from scraped-examples.md

Fixes rust-lang#110711