Previously, the signal mask is always reset when a child process is
started. This breaks tools like `nohup` which expect `SIGHUP` to be
blocked.

With this change, the default behavior changes to inherit the signal mask.

This also changes the signal disposition for `SIGPIPE` to only be
changed if the `#[unix_sigpipe]` attribute isn't set.

Splits proc_macro::Span::source_text into a new feature gate and stabilizes it.

This change tweaks the CSS to apply most of its styles to `.sidebar h2`,
cleaning up a few redundant rules from `.mobile-topbar .location` and
restoring useful navigation aids in mobile mode.

This allows porting uses of span_suggestions() to diagnostic structs.

Doesn't work for multipart_suggestions() because the rank would be
reversed - the struct would specify multiple spans, each of which has
multiple possible replacements, while multipart_suggestions() creates
multiple possible replacements, each with multiple spans.

(But not fn() -> !, which is stable.)

…thomcc

Change process spawning to inherit the parent's signal mask by default

Previously, the signal mask was always reset when a child process is
started. This breaks tools like `nohup` which expect `SIGHUP` to be
blocked for all transitive processes.

With this change, the default behavior changes to inherit the signal mask.

This also changes the signal disposition for `SIGPIPE` to only be changed if the `#[unix_sigpipe]` attribute isn't set.

…text, r=petrochenkov

Stabilize proc_macro::Span::source_text

Splits `proc_macro::Span::source_text` into a new feature gate and stabilizes it. The [FCP is complete](rust-lang#101991 (comment)).

```Rust
impl Span {
    pub fn source_text(&self) -> Option<String>;
}
```

Closes rust-lang#101991

…vidtwco

Diagnostic derives: allow specifying multiple alternative suggestions

This allows porting `span_suggestions()` to diagnostic structs.

Doesn't work for `multipart_suggestions()` because the rank would be reversed - the struct would specify multiple spans, each of which has multiple possible replacements, while `multipart_suggestions()` creates multiple possible replacements, each with multiple spans.

…r=GuillaumeGomez

rustdoc: remove class name `location` from sidebar sibling nav

Preview: https://notriddle.com/notriddle-rustdoc-demos/sidebar-location/std/vec/struct.Vec.html

This change tweaks the CSS to apply most of its styles to `.sidebar h2`, cleaning up a few redundant rules from `.mobile-topbar .location` and restoring useful navigation aids in mobile mode.

## Before

![location-before](https://user-images.githubusercontent.com/1593513/196521014-d8730830-c3a2-4ed7-9266-05454cd31e05.png)

## After

![location-after](https://user-images.githubusercontent.com/1593513/196521020-75ec1fa5-b3dc-4c5d-97b6-afccb5fbe00a.png)

…leanup, r=notriddle

Clean up codeblock-tooltip rustdoc-gui test

r? `@notriddle`

…, r=lcnr

Allow #[unstable] impls for fn() with unstable abi.

This allows `#[unstable]` trait impls for `extern "unwind-C" fn()`, based on the fact that that abi and therefore that type is unstable.

See rust-lang#101263 (comment)