…to preserve all UB that the native intrinsic would have

Very minor thing, obviously, but I randomly saw this unnecessary cast showing up in the UbChecks, so might as well get rid of it.

As of 124114 it's exactly the same in codegen, so might as well not use `unsafe`.

Note that this is only for *unsigned*, since the overflow conditions for `iN::checked_sub` are more complicated.

…nton

Reduce code size of `thread::set_current`

rust-lang#123265 introduced a rather large binary size regression, because it added an `unwrap()` call on a `Result<(), Thread>`, which in turn pulled its rather heavy `Debug` implementation. This PR fixes this by readding the `rtassert!` that was removed.

…ChrisDenton

Move thread parking to `sys::sync`

Part of rust-lang#117276.

I'll leave the platform-specific API abstractions in `sys::pal`, as per the initial proposal. I'm not entirely sure whether we'll want to keep it that way, but that remains to be seen.

r? ``@ChrisDenton`` (if you have time)

…dy, r=RalfJung

Let miri and const eval execute intrinsics' fallback bodies

fixes rust-lang/miri#3397

r? ``@RalfJung``

…r, r=tmandry

Set non-leaf frame pointers on Fuchsia targets

This is part of our work to enable shadow call stack sanitization on Fuchsia, see [this Fuchsia issue](https://g-issues.fuchsia.dev/issues/327643884).

r? ``@tmandry``

…pointer-coercion-happens, r=compiler-errors

We do not coerce `&mut &mut T -> *mut mut T`

Resolves rust-lang#34117 by declaring it to be "working as intended" until someone RFCs it or whatever other lang proposal would be required. It seems a bit of a footgun, but perhaps there are strong reasons to allow it anyways. Seeing as how I often have to be mindful to not allow a pointer to coerce the wrong way in my FFI work, I am inclined to think not, but perhaps it's fine in some use-case and that's actually more common?

…m, r=jieyouxu

Rewrite `rustdoc-determinism` test in Rust

Rewrite the `rustdoc-determinism` test from rust-lang#121876.

r? `@jieyouxu`

Remove an unnecessary cast

Very minor thing, obviously, but I randomly saw this unnecessary cast showing up in the UbChecks, so might as well get rid of it.

…strieb

Docs: suggest `uN::checked_sub` instead of check-then-unchecked

As of rust-lang#124114 it's exactly the same in codegen, so might as well not use `unsafe`.

Note that this is only for *unsigned*, since the overflow conditions for `iN::checked_sub` are more complicated.