Remove `Errors` section from `var_os` documentation

Re-introduced some of the former errors as situations where `None` is returned.

Co-authored-by: León Orell Valerian Liehr <me@fmease.dev>

one is enough

Original `var_os` description said that it _may_ return an error if the value contains `=` or NUL. Let's make no promises on the `None` return value in these situation either, keep it in the [potential mood](https://en.wikipedia.org/wiki/Grammatical_mood#Potential).

Tests marked `// force-host` were using the default linker, even if a
custom linker was configured in config.toml.

This change adds a new flag, --host-linker, to compiletest, and renames
--linker to --target-linker.

This functionality is already tested in `hash-item-expansion.goml`,
and was implemented twice:

* First, in code that ran at load time and at hash change:
  917cdd2

* Later, the hash change event handler was itself run at load time,
  and the code handling both cases diverged in implementation,
  though their behavior still matches pretty well:
  f66a331

Further referring to `var_os` as a "function" (like in `var`), rather than "method".

Previously, we would never build the target std, only the host std.

Initial support for loongarch64-unknown-linux-gnu

Hi, We hope to add a new port in rust for LoongArch.

LoongArch intro
LoongArch is a RISC style ISA which is independently designed by Loongson
Technology in China. It is divided into two versions, the 32-bit version (LA32)
and the 64-bit version (LA64). LA64 applications have application-level
backward binary compatibility with LA32 applications. LoongArch is composed of
a basic part (Loongson Base) and an expanded part. The expansion part includes
Loongson Binary Translation (LBT), Loongson VirtualiZation (LVZ), Loongson SIMD
EXtension (LSX) and Loongson Advanced SIMD EXtension(LASX).

Currently the LA464 processor core supports LoongArch ISA and the Loongson
3A5000 processor integrates 4 64-bit LA464 cores. LA464 is a four-issue 64-bit
high-performance processor core. It can be used as a single core for high-end
embedded and desktop applications, or as a basic processor core to form an
on-chip multi-core system for server and high-performance machine applications.

Documentations:
ISA:
https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html
ABI:
https://loongson.github.io/LoongArch-Documentation/LoongArch-ELF-ABI-EN.html
More docs can be found at:
https://loongson.github.io/LoongArch-Documentation/README-EN.html

Since last year, we have locally adapted two versions of rust, rust1.41 and rust1.57, and completed the test locally.
I'm not sure if I'm submitting all the patches at once, so I split up the patches and here's one of the commits

…returns-an-error, r=cuviper

Remove Errors section from var_os docs

Remove `Errors` section from `var_os` documentation, fixes rust-lang#109893

Rename tests/ui/unique to tests/ui/box/unit

fixes rust-lang#109878

Since tests/ui/box already exists, I have temporarily named it boxed-box, but if another name sounds better, please let me know.

…esleywiser

Pass host linker to compiletest.

Tests marked `// force-host` were using the default linker, even if a custom linker was configured in config.toml.

This change adds a new flag, --host-linker, to compiletest, and renames --linker to --target-linker.

 Reword the docstring in todo! macro definition, fixing a typo

…ertlarsan68

Fix `x test ui --target foo` when download-rustc is enabled

Previously, we would never build the target std, only the host std:

```
; x t tests/ui/attributes --target wasm32-unknown-unknown
Building bootstrap
    Finished dev [unoptimized] target(s) in 0.02s
Building stage0 library artifacts (x86_64-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.08s
Building tool compiletest (stage0)
    Finished release [optimized] target(s) in 0.09s
Check compiletest suite=ui mode=ui (x86_64-unknown-linux-gnu -> wasm32-unknown-unknown)
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error { depth: 0, inner: Io { path: Some("/home/jyn/src/rust2/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/wasm32-unknown-unknown/lib"), err: Os { code: 2, kind: NotFound, message: "No such file or directory" } } }', src/tools/compiletest/src/main.rs:842:31
```

Helps with rust-lang#81930.

…ansmute, r=oli-obk

Support safe transmute in new solver

Basically copies the same implementation as the old solver, but instead of looking for param types, we look for type or const placeholders.

Fix typos in librustdoc, tools and config files

I used [`typos`](https://github.com/crate-ci/typos) to fix all typos, minus the ones present in rust-lang#110153 and in rust-lang#110154.

Refs rust-lang#110150

…, r=GuillaumeGomez

rustdoc: remove redundant expandSection code from main.js

This functionality is already tested in `hash-item-expansion.goml`, and was implemented twice:

* First, in code that ran at load time and at hash change: 917cdd2

* Later, the hash change event handler was itself run at load time, and the code handling both cases diverged in implementation, though their behavior still matches pretty well: f66a331

…ad-buf, r=cuviper

kmc-solid: Implement `Socket::read_buf`

Follow-up to rust-lang#108326. Implements `Socket::read_buf` for the [`*-kmc-solid_*`](https://doc.rust-lang.org/nightly/rustc/platform-support/kmc-solid.html) Tier 3 targets.