This reverts commit faac70b.

As discovered by Mara in rust-lang#110897, our TLS implementation is a total mess. In the past months, I have simplified the actual macros and their expansions, but the majority of the complexity comes from the platform-specific support code needed to create keys and register destructors. In keeping with rust-lang#117276, I have therefore moved all of the `thread_local_key`/`thread_local_dtor` modules to the `thread_local` module in `sys` and merged them into a new structure, so that future porters of `std` can simply mix-and-match the existing code instead of having to copy the same (bad) implementation everywhere. The new structure should become obvious when looking at `sys/thread_local/mod.rs`.
Unfortunately, the documentation changes associated with the refactoring have made this PR rather large. That said, this contains no functional changes except for two small ones:
* the key-based destructor fallback now, by virtue of sharing the implementation used by macOS and others, stores its list in a `#[thread_local]` static instead of in the key, eliminating one indirection layer and drastically simplifying its code.
* I've switched over ZKVM (tier 3) to use the same implementation as WebAssembly, as the implementation was just a way worse version of that
Please let me know if I can make this easier to review! I know these large PRs aren't optimal, but I couldn't think of any good intermediate steps.
@rustbot label +A-thread-locals

Signed-off-by: onur-ozkan <work@onurozkan.dev>

I believe this was changed a while ago in rust-lang/promote-release#14.

When using `symlink_dir`, it first removes the existing link with `remove_dir`.
However, if the path isn't a link and contains files, `remove_dir` fails
with "DirectoryNotEmpty", which causes the symbolic linking to fail as well.
We have this problem on linking 'rustlib/rust' because it contains files as an
actual directory.
Signed-off-by: onur-ozkan <work@onurozkan.dev>

If `codegen-backends` is missing "cranelift" and "gcc" (which is common),
bootstrap will now only show this warning during `dist` and `install` steps,
or if codegen-backends was explicitly called for build.
Signed-off-by: onur-ozkan <work@onurozkan.dev>

This is already handled from bootstrap at
https://github.com/rust-lang/rust/blob/a1ca449981e3b8442e358026437b7bedb9a1458e/src/bootstrap/src/utils/helpers.rs#L504-L506.
Signed-off-by: onur-ozkan <work@onurozkan.dev>

So we can omit the `token::` qualifier, which gives more space to some
cramped code.

Merge `PatParam`/`PatWithOr`, and `Expr`/`Expr2021`, for a few reasons.
- It's conceptually nice, because the two pattern kinds and the two
 expression kinds are very similar.
- With expressions in particular, there are several places where both
 expression kinds get the same treatment.
- It removes one unreachable match arm.
- Most importantly, for rust-lang#124141 I will need to introduce a new type
 `MetaVarKind` that is very similar to `NonterminalKind`, but records a
 couple of extra fields for expression metavars. It's nicer to have a
 single `MetaVarKind::Expr` expression variant to hold those extra
 fields instead of duplicating them across two variants
 `MetaVarKind::{Expr,Expr2021}`. And then it makes sense for patterns
 to be treated the same way, and for `NonterminalKind` to also be
 treated the same way.
I also clarified the comments, because I have long found them a little
hard to understand.

...-Simulacrum
tidy: skip submodules if not present for non-CI environments
Right now tidy requires rustc-perf to be fetched as it checks its license, but this doesn't make sense for most contributors since rustc-perf is a dist-specific tool and its license will not change frequently, especially during compiler development. This PR makes tidy to skip rustc-perf if it's not fetched and if it's not running in CI.
Applies rust-lang#126225 (comment) and reverts rust-lang#126225.

... r=Mark-Simulacrum
std: refactor the TLS implementation
As discovered by Mara in rust-lang#110897, our TLS implementation is a total mess. In the past months, I have simplified the actual macros and their expansions, but the majority of the complexity comes from the platform-specific support code needed to create keys and register destructors. In keeping with rust-lang#117276, I have therefore moved all of the `thread_local_key`/`thread_local_dtor` modules to the `thread_local` module in `sys` and merged them into a new structure, so that future porters of `std` can simply mix-and-match the existing code instead of having to copy the same (bad) implementation everywhere. The new structure should become obvious when looking at `sys/thread_local/mod.rs`.
Unfortunately, the documentation changes associated with the refactoring have made this PR rather large. That said, this contains no functional changes except for two small ones:
* the key-based destructor fallback now, by virtue of sharing the implementation used by macOS and others, stores its list in a `#[thread_local]` static instead of in the key, eliminating one indirection layer and drastically simplifying its code.
* I've switched over ZKVM (tier 3) to use the same implementation as WebAssembly, as the implementation was just a way worse version of that
Please let me know if I can make this easier to review! I know these large PRs aren't optimal, but I couldn't think of any good intermediate steps.
`@rustbot` label +A-thread-locals

...k-Simulacrum
Update outdated README in build-manifest.
I believe this was changed a while ago in rust-lang/promote-release#14.

...imulacrum
less bootstrap warnings
This is how the build logs looks like currently:
```sh
$ x build
Building bootstrap
 Compiling bootstrap v0.0.0 (/home/nimda/devspace/onur-ozkan/rust/src/bootstrap)
 Finished `dev` profile [unoptimized] target(s) in 3.43s
WARNING: no codegen-backends config matched the requested path to build a codegen backend. HELP: add backend to codegen-backends in config.toml.
WARNING: creating symbolic link `/home/nimda/devspace/.other/rustc-builds/build/x86_64-unknown-linux-gnu/stage2/lib/rustlib/rustc-src/rust` to `/home/nimda/devspace/onur-ozkan/rust` failed with File exists (os
error 17)
Creating a sysroot for stage2 compiler (use `rustup toolchain link 'name' build/host/stage2`)
WARNING: creating symbolic link `/home/nimda/devspace/.other/rustc-builds/build/x86_64-unknown-linux-gnu/ci-rustc-sysroot/lib/rustlib/rustc-src/rust` to `/home/nimda/devspace/onur-ozkan/rust` failed with File e
xists (os error 17)
Building tool rustdoc (stage1 -> stage2, x86_64-unknown-linux-gnu)
 Compiling rustdoc v0.0.0 (/home/nimda/devspace/onur-ozkan/rust/src/librustdoc)
 Compiling rustdoc-tool v0.0.0 (/home/nimda/devspace/onur-ozkan/rust/src/tools/rustdoc)
 Finished `release` profile [optimized + debuginfo] target(s) in 13.57s
Build completed successfully in 0:00:17
```
This PR removes artifact linking warnings and only shows the codegen-backend warning if explicitly called or during Dist or Install steps.

...mulacrum
remove `GIT_DIR` handling in pre-push hook
This is already handled from bootstrap: https://github.com/rust-lang/rust/blob/a1ca449981e3b8442e358026437b7bedb9a1458e/src/bootstrap/src/utils/helpers.rs#L504-L506 

...iler-errors
make unsized_fn_params an internal feature
As suggested [here](rust-lang#123894 (comment)).
r? `@compiler-errors`
Fixes rust-lang#123887 (kind of -- ICEs on internal features are considered acceptable so this issue is not-a-bug once this PR lands)

...compiler-errors
don't ICE when encountering an extern type field during validation
"extern type" is a pain that keeps on giving...
Fixes rust-lang#126814
r? `@oli-obk`

...errors
delegation: Do not crash on qpaths without a trait
Fixes rust-lang#126742 

...r=compiler-errors
Rework pattern and expression nonterminal kinds.
Some tweaks to `NonterminalKind` that will assist with rust-lang#124141. Details in the individual commits.
r? compiler-errors
cc `@eholk`