Revert some changes from #51917 to fix #52317.

src/bootstrap/bin/rustdoc.rs

@@ -35,7 +35,7 @@ fn main() {
     };
 
     let mut dylib_path = bootstrap::util::dylib_path();
-    dylib_path.insert(0, PathBuf::from(libdir));
+    dylib_path.insert(0, PathBuf::from(libdir.clone()));
 
     let mut cmd = Command::new(rustdoc);
     cmd.args(&args)
@@ -69,6 +69,7 @@ fn main() {
 
     if verbose > 1 {
         eprintln!("rustdoc command: {:?}", cmd);
+        eprintln!("libdir: {:?}", libdir);
     }
 
     std::process::exit(match cmd.status() {

src/bootstrap/builder.rs

@@ -825,7 +825,7 @@ impl<'a> Builder<'a> {
             cargo.env("RUSTC_ERROR_FORMAT", error_format);
         }
         if cmd != "build" && cmd != "check" && want_rustdoc {
-            cargo.env("RUSTDOC_LIBDIR", &libdir);
+            cargo.env("RUSTDOC_LIBDIR", self.sysroot_libdir(compiler, self.config.build));
         }
 
         if mode.is_tool() {