Rollup merge of rust-lang#101322 - ChrisDenton:internal-doc, r=Mark-Simulacrum

Fix internal doc link

The doc link from `DedupSortedIter` to `BTreeMap::bulk_build_from_sorted_iter` was broken when building internal documentation,

This prevented me from building internal documentation locally:

```
R:\Rust\rust> $env:RUSTDOCFLAGS="--document-private-items"
R:\Rust\rust> x doc library/std --open --stage 0
Building rustbuild
   Compiling bootstrap v0.0.0 (R:\Rust\rust\src\bootstrap)
    Finished dev [unoptimized] target(s) in 3.15s
Documenting stage0 std (x86_64-pc-windows-msvc)
 Documenting core v0.0.0 (R:\Rust\rust\library\core)
    Finished release [optimized] target(s) in 36.42s
    Checking core v0.0.0 (R:\Rust\rust\library\core)
    Checking rustc-std-workspace-core v1.99.0 (R:\Rust\rust\library\rustc-std-workspace-core)
    Checking compiler_builtins v0.1.79
 Documenting alloc v0.0.0 (R:\Rust\rust\library\alloc)
error: unresolved link to `BTreeMap::bulk_build_from_sorted_iter`
 --> library\alloc\src\collections\btree\dedup_sorted_iter.rs:6:15
  |
6 | /// Used by [`BTreeMap::bulk_build_from_sorted_iter`].
  |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no item named `BTreeMap` in scope
  |
  = note: `-D rustdoc::broken-intra-doc-links` implied by `-D warnings`

error: could not document `alloc`
```

Author: matthiaskrgr

library/alloc/src/collections/btree/dedup_sorted_iter.rs

@@ -3,7 +3,9 @@ use core::iter::Peekable;
 /// A iterator for deduping the key of a sorted iterator.
 /// When encountering the duplicated key, only the last key-value pair is yielded.
 ///
-/// Used by [`BTreeMap::bulk_build_from_sorted_iter`].
+/// Used by [`BTreeMap::bulk_build_from_sorted_iter`][1].
+///
+/// [1]: crate::collections::BTreeMap::bulk_build_from_sorted_iter
 pub struct DedupSortedIter<K, V, I>
 where
     I: Iterator<Item = (K, V)>,

src/ci/docker/host-x86_64/mingw-check/Dockerfile

@@ -45,7 +45,8 @@ ENV SCRIPT python3 ../x.py --stage 2 test src/tools/expand-yaml-anchors && \
            python3 ../x.py test --stage 0 src/tools/compiletest && \
            python3 ../x.py test --stage 2 src/tools/tidy && \
            python3 ../x.py test --stage 0 core alloc std test proc_macro && \
-           python3 ../x.py doc --stage 0 library/test && \
+           # Build both public and internal documentation.
+           RUSTDOCFLAGS="--document-private-items" python3 ../x.py doc --stage 0 library/test && \
            /scripts/validate-toolstate.sh && \
            /scripts/validate-error-codes.sh && \
            reuse lint && \