Remove the FIXME and keep `CRATE_HIR_ID` being its own parent.
This scheme turned out to be more practical than having an `Option` on closer inspection.

Also make `hir_owner_parent` more readable.

Make the polymorphic is_nonoverlapping private

Fix assert_unsafe_precondition doc typos

Add docs for intrinsics::debug_assertions

Create try_new function for ThinBox

The `allocator_api` feature has proven very useful in my work in the FreeBSD kernel. I've found a few places where a `ThinBox` rust-lang#92791 would be useful, but it must be able to be fallibly allocated for it to be used in the kernel.

This PR proposes a change to add such a constructor for ThinBox.

ACP: rust-lang/libs-team#213

Make cmath.rs a single file

It makes sense to have this all in one file. There's essentially only one target that has missing symbols and that's easy enough to handle inline.

Note that the Windows definitions used to use `c_float` and `c_double` whereas the other platforms all used `f32` and `f64`. They've now been made consistent. However, `c_float` and `c_double` have the expected definitions on all Windows platforms we support.

hir: Refactor getters for HIR parents

See individual commits.

I ended up removing on of the FIXMEs from rust-lang#120206 instead of addressing it.

…=cuviper

add note on comparing vtables / function pointers

Fixes rust-lang#99388
Fixes rust-lang#117047

…r-errors

interpret/visitor: ensure we only see normalized types

[Prior discussion on Zulip](https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/topic/Normalization.20after.20field.20projection)
r? `@compiler-errors`

…up, r=RalfJung

assert_unsafe_precondition cleanup

I moved the polymorphic `is_nonoverlapping` into the `Cell` function that uses it and renamed `intrinsics::is_nonoverlapping_mono` to just `intrinsics::is_nonoverlapping`.

We now also have some docs for `intrinsics::debug_assertions`.

r? RalfJung

…ure, r=oli-obk

Encode `coroutine_for_closure` for foreign crates

Async closures (and "coroutine closures" in general) need to have their child coroutine encoded. This PR does that.

r? oli-obk

…links-and-info, r=JohnTitor

[docs] Update armv6k-nintendo-3ds platform docs for outdated info

Mostly just fixing links and references to renamed crates, but also updating a bit of outdated info as well.

CC `@Meziu` `@AzureMarker`