[rustdoc] When using `-Zbuild-std`, documentation does not link to `core`/`std` and does not attempt to build docs for them

[ThePuzzlemaker]

I tried this code:

/// [`usize`]
///
/// [`usize`][core::usize]
pub struct Foo;

Built with cargo +nightly doc --target x86_64-unknown-linux-gnu -Zbuild-std

I expected to see this happen: Rustdoc links properly to traits and intra-doc links, as shown when built with cargo +nightly doc --target x86_64-unknown-linux-gnu

Instead, this happened: When built with -Zbuild-std, rustdoc does not link to these traits or properly resolve intra-doc links, and does not attempt to rectify this by building docs for core or std:

Meta

This bug is not applicable to stable due to its use of -Zbuild-std

rustc --version --verbose:

rustc 1.75.0-nightly (fcab24817 2023-10-13)
binary: rustc
commit-hash: fcab24817c72ffbd6ffb66d92b7ddc0d3ee4d2f0
commit-date: 2023-10-13
host: x86_64-unknown-linux-gnu
release: 1.75.0-nightly
LLVM version: 17.0.2

@rustbot modify labels: +A-rustdoc-ui +-Z-build-std +requires-nightly

[rustbot]

Error: Label -Z-build-std can only be set by Rust team members

Please file an issue on GitHub at triagebot if there's a problem with this bot, or reach out on #t-infra on Zulip.

[ThePuzzlemaker]

@rustbot modify labels: +A-rustdoc-ui +requires-nightly