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

[Andy Kaylor via cfe-commits]

================
@@ -0,0 +1,51 @@
+//===- ASTAttrInterfaces.td - CIR AST Interface Definitions -----*- 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 MLIR_CIR_INTERFACES_AST_ATTR_INTERFACES
----------------
andykaylor wrote:

```suggestion
#ifndef MLIR_CIR_INTERFACES_ASTATTRINTERFACES_TD
```
Here I looked at `CIRTypeInterfaces.td`, `CIROpInterfaces.td`, and `CIRLoopOpInterface.td`. They all keep the base filename intact. `CIRLoopOpInterface.td` omits the `_TD`, but the other two have it.

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