Only copy library dir for stdlib

When building as part of rust, the sysroot source dir is symlinked to
the main source dir, which contains the build dir to which we are likely
copying.

Author: bjorn3

build_system/prepare.rs

@@ -268,7 +268,12 @@ pub(crate) fn apply_patches(dirs: &Dirs, crate_name: &str, source_dir: &Path, ta
 
     remove_dir_if_exists(target_dir);
     fs::create_dir_all(target_dir).unwrap();
-    copy_dir_recursively(source_dir, target_dir);
+    if crate_name == "stdlib" {
+        fs::create_dir(target_dir.join("library")).unwrap();
+        copy_dir_recursively(&source_dir.join("library"), &target_dir.join("library"));
+    } else {
+        copy_dir_recursively(source_dir, target_dir);
+    }
 
     init_git_repo(target_dir);