Just as `get_mut` is the inverse of `from_mut`, `get_mut_slice` is the
inverse of `from_mut_slice`.

…into it

This reduces binary size from 10.1MiB (6.2MiB for just rustbuild code)
to 9.7MiB (5.8MiB for just rustbuild code).

This also reduces compile time from ~6.1s for incr recompilation to ~5.6s.

There is still a lot of
unnecessary code due to the toml crate monomorphizing every
deserialization impl 5 times.

This reduces binary size from 9.7MiB (5.8MiB for just rustbuild code)
to 9.3MiB (5.3MiB for just rustbuild code).

This doesn't reduce compile time in a statistically significant way.

These crates aren't necessary for building the standard library. This
saves 30MB of disk space.

Fixes rust-lang#94906

Implement `BITS` constant for non-zero integers

This adds the associated [`BITS`](https://doc.rust-lang.org/stable/std/primitive.usize.html#associatedconstant.BITS) constant to `NonZero{U,I}{8,16,32,64,128,size}`.

This is useful when a type alias refers to either a regular or non-zero integer.

…clibceabi, r=Mark-Simulacrum

Update armv7-unknown-linux-uclibceabi platform support page.

A few edits and fixes to the support page for the armv7-unknown-linux-uclibceabi target.

…r=Mark-Simulacrum

Add `Atomic*::get_mut_slice`

This PR adds the inverse of `Atomic*::from_mut_slice` introduced in rust-lang#94384 with the following API:
```rust
// core::sync::atomic

impl Atomic* {
    fn get_mut_slice(this: &mut [Self]) -> &mut [*];
}
```

cc `@cuviper`

-----

For now I've used the same tracking issue as `Atomic*::from_mut_slice`, should I open a new one?

…mulacrum

Reduce rustbuild bloat caused by serde_derive

This reduces the size of the `.text` section from 10.1MiB (6.2MiB for just rustbuild code) to 9.3MiB (5.3MiB for just rustbuild code).

This also reduces compile time from ~6.1s for incr recompilation to ~5.6s.

r? `@Mark-Simulacrum`

…r=Mark-Simulacrum

Omit stdarch test crates from the rust-src component

These crates aren't necessary for building the standard library. This saves 30MB of disk space.

Fixes rust-lang#94906