[llvm] [CAS] Add UnifiedOnDiskCache and OnDiskCAS (PR #114103)

[Justin Bogner via llvm-commits]

================
@@ -215,9 +223,39 @@ class ObjectStore {
     return Data.size();
   }
 
+  /// Set the size for limiting growth of on-disk storage. This has an effect
+  /// for when the instance is closed.
+  ///
+  /// Implementations may be not have this implemented.
----------------
bogner wrote:

```suggestion
  /// Implementations may leave this unimplemented.
```

https://github.com/llvm/llvm-project/pull/114103