This enables usage of the offset_of!() macro in the compiler,
through the wrappers in memoffset and then in field-offset.

Soft deprecate old python versions to give users a warning that
eventually it may not be supported.

…-Simulacrum

bootstrap: Disallow `--exclude test::std`

Use the top-level Kind to determine whether Steps are excluded.

Previously, this would use the `Kind` passed to `--exclude` (and not do any filtering at all if no kind was passed).
That meant that `x test linkchecker --exclude std` would fail - you had to explicitly say `--exclude test::std`.

Change bootstrap to use the top-level Kind instead, which does the right thing automatically.
Note that this breaks things like `x test --exclude doc::std`, but I'm not sure why you'd ever want to do that.

There's a lot of churn here, but the 1-line change in the first commit is the actual behavior change, the rest is just cleanup.

Fixes rust-lang#103201. Note that this effectively reverts most of rust-lang#91965.

cc `@pietroalbini`

…Simulacrum

Update field-offset and enable unstable_offset_of

This makes the compiler use the builtin `offset_of!()` macro, through the wrappers in memoffset and then in field-offset.

cc  rust-lang#111839

ci: Upgrade loongarch64-linux-gnu GCC to 13.1.0

This PR upgrades GCC to 13.1.0 for the `loongarch64-unknown-linux-gnu` target. This upgrade was suggested in a previous review discussion: rust-lang#110519 (comment)

…-span-order, r=petrochenkov

Adjust span labels for `HIDDEN_GLOB_REEXPORTS`

Addresses rust-lang#111378 (comment).

### Before This PR

The possibility that the private item comes before the glob re-export was not account for, causing the span label messages to say "but private item here shadows it" before "the name `Foo` in the type namespace is supposed to be publicly re-exported here".

### After This PR

```rust
warning: private item shadows public glob re-export
  --> $DIR/hidden_glob_reexports.rs:9:5
   |
LL |     struct Foo;
   |     ^^^^^^^^^^^ the private item here shadows the name `Foo` in the type namespace
...
LL |     pub use self::inner::*;
   |             -------------- but it is supposed to be publicly re-exported here
   |
   = note: `#[warn(hidden_glob_reexports)]` on by default

warning: private item shadows public glob re-export
  --> $DIR/hidden_glob_reexports.rs:27:9
   |
LL |     pub use self::inner::*;
   |             -------------- the name `Foo` in the type namespace is supposed to be publicly re-exported here
LL |
LL |     use self::other::Foo;
   |         ^^^^^^^^^^^^^^^^ but the private item here shadows it
```

…imulacrum

Add deprecation warning to python versions <3.6 in x.py

Introduced based on conversation on Zulip. This is a repeat of rust-lang#110439 with two changes:

- Warning rather than exit
- Can be suppressed via an environment variable

The min to not get the warning is set to 3.6 because that's a fairly recent "old" version (went EOL in 2021) and it's the first version to support useful modern features like f-strings and type hints.

cc `@Nilstrieb` (author of rust-lang#110439) and `@Mark-Simulacrum` (reviewer of that PR)