Previously, the types looked like this:

- None means this is not an associated item (but may be a variant field)
- Some(Err) means this is known to be an error. I think the only way that can happen is if it resolved and but you had your own anchor.
- Some(Ok(_, None)) was impossible.

Now, this returns a nested Option and does the error handling and
fiddling with the side channel in the caller. As a side-effect, it also
removes duplicate error handling.

This has one small change in behavior, which is that
`resolve_primitive_associated_item` now goes through `variant_field` if
it fails to resolve something.  This is not ideal, but since it will be
quickly rejected anyway, I think the performance hit is worth the
cleanup.

This also fixes a bug where struct fields would forget to set the side
channel, adds a test for the bug, and ignores `private_intra_doc_links`
in rustc_resolve (since it's always documented with
--document-private-items).

Since compiler/ always passes --document-private-items, it's ok to link
to items that are private.

Otherwise no one will be able to find the setting.

Add `x.py setup tools` which enables `download-rustc` by default

Helps with rust-lang#81930. I know I said in that issue that I should fix that rebasing rebuilds bootstrap, but the compile time improvement is so good I think it's ok to leave that fix for later (I still plan to work on it). I think all the outright bugs have been fixed :)

This builds on rust-lang#83368 so I can set the option to `if-unchanged`.

r? `@Mark-Simulacrum`

Add `__CxxFrameHandler3` in `panic_abort`

Fix rust-lang#54137

<del>I initially tried to forward to `__CxxFrameHandler3` from `rust_eh_personality`, but later I found that LLVM uses handler names to distinguish exception type. Therefore I choose to add `__CxxFrameHandler3` in `panic_abort`. Anyway it solves the link problem, and this function will never be called.</del>

It seems that the original issue was solved, but still adding these tests.

rustdoc: Cleanup handling of associated items for intra-doc links

Helps with rust-lang#83761 (right now the uses of the resolver are all intermingled with uses of the tyctxt). Best reviewed one commit at a time.

r? `@bugadani` maybe? Feel free to reassign :)

…=jonas-schievink

⬆️ rust-analyzer

…crum

Document compiler/ with -Aprivate-intra-doc-links

Since compiler/ always passes --document-private-items, it's ok to link to items that are private.