This is another step toward making opt-dist work in sandboxed environments

opt-dist verifies the final built rustc against a subset of rustc test
suite. However it overwrote the pre-existing `config.toml` [^1],
and that results in ./vendor/ directory removed [^2].

Instead of overwriting, this patch use `--set <config-value>` to
override paths to rustc / cargo / llvm-config.

[^1]: https://github.com/rust-lang/rust/blob/606afbb617a2949a4e35c4b0258ff94c980b9451/src/tools/opt-dist/src/tests.rs#L62-L77
[^2]: https://github.com/rust-lang/rust/blob/8679004993f08807289911d9f400f4ac4391d2bc/src/bootstrap/bootstrap.py#L1057

… r=Mark-Simulacrum

tidy: stop special-casing tests/ui entry limit

It is genuinely more annoying to have this error, now that this value is below the general `ENTRY_LIMIT` cap, when one is trying to clean out tests from tests/ui! This code has served its purpose well, let it rest now rather than force it to continue haunting us.

…=Mark-Simulacrum

Create a triagebot ping group for Rust for Linux

Corresponding rustc-dev-guide PR [here](rust-lang/rustc-dev-guide#1984). Discussed on [Zulip](https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/Testing.20Rust.20for.20Linux.20in.20our.20CI).

…toml, r=Kobzol

fix(opt-dist): respect existing config.toml

This is another step toward making opt-dist work in sandboxed environments. See also <rust-lang#125465>.

opt-dist verifies the final built rustc against a subset of rustc test
suite. However it overwrote the pre-existing `config.toml` [^1],
and that results in ./vendor/ directory removed [^2].

Instead of overwriting, this patch use `--set <config-value>` to
override paths to rustc / cargo / llvm-config.

[^1]: https://github.com/rust-lang/rust/blob/606afbb617a2949a4e35c4b0258ff94c980b9451/src/tools/opt-dist/src/tests.rs#L62-L77
[^2]: https://github.com/rust-lang/rust/blob/8679004993f08807289911d9f400f4ac4391d2bc/src/bootstrap/bootstrap.py#L1057

Stop SRoA'ing `DynMetadata` in MIR

Fixes rust-lang#125506

cleanup dependence of `ExtCtxt` in transcribe when macro expansion

part of rust-lang#125356
We can remove `transcribe`’s dependence on `ExtCtxt` to facilitate subsequent work (such as moving macro expansion into the incremental compilation system)

r? ````@petrochenkov````
Thanks for the reviewing!

…ific, r=Mark-Simulacrum

Also mention my-self for other check-cfg docs changes

This PR adds a mention for my-self for the recently added `src/doc/rustc/src/check-cfg` directory.

*I had to add a second mention just for the directory since [`Path::starts_with`](https://doc.rust-lang.org/std/path/struct.Path.html#method.starts_with) as used by [triagebot](https://github.com/rust-lang/triagebot/blob/48f29f351cae774caa90f555fbbc6d0df7dce80e/src/handlers/mentions.rs#L69), matches on path components and so can never return true for a file and directory at the same time.*

…=workingjubilee

Simplify the `unchecked_sh[lr]` ub-checks a bit

It can use the constant in the check, rather than passing it as a parameter.