Auto merge of #95502 - jyn514:doc-rustc, r=Mark-Simulacrum

Fix `x doc compiler/rustc`

This also has a few cleanups to `doc.rs`. The last two commits I don't care about, but the first commit I'd like to keep - it will be very useful for https://github.com/rust-lang/rust/issues/44293.

Fixes https://github.com/rust-lang/rust/issues/95447.

src/bootstrap/lib.rs

@@ -302,7 +302,9 @@ pub struct Build {
     ar: HashMap<TargetSelection, PathBuf>,
     ranlib: HashMap<TargetSelection, PathBuf>,
     // Miscellaneous
+    // allow bidirectional lookups: both name -> path and path -> name
     crates: HashMap<Interned<String>, Crate>,
+    crate_paths: HashMap<PathBuf, Interned<String>>,
     is_sudo: bool,
     ci_env: CiEnv,
     delayed_failures: RefCell<Vec<String>>,
@@ -492,6 +494,7 @@ impl Build {
             ar: HashMap::new(),
             ranlib: HashMap::new(),
             crates: HashMap::new(),
+            crate_paths: HashMap::new(),
             is_sudo,
             ci_env: CiEnv::current(),
             delayed_failures: RefCell::new(Vec::new()),