[clang] [CIR] Add ASTVarDeclInterface for AST attribute access (PR #179825)

[Andy Kaylor via cfe-commits]

================
@@ -0,0 +1,22 @@
+//===- ASTAttrInterfaces.h - CIR AST Interfaces -----------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef CLANG_CIR_INTERFACES_AST_ATTR_INTERFACES_H
----------------
andykaylor wrote:

```suggestion
#ifndef CLANG_CIR_INTERFACES_ASTATTRINTERFACES_H
```
I can see benefits to this either way, but keeping the filename intact seems to follow established conventions.

https://github.com/llvm/llvm-project/pull/179825