[clang] [clang][ASTImport] fix issue on anonymous enum import (PR #93923)

[Qizhi Hu via cfe-commits]

jcsxky wrote:

> Does this work on the following code?
> 
> ```
>      struct A {
>         enum { E1,E2 } x;
>         enum { E3,E4 } y;
>       };
> ```

I have updated testcase according to your suggestion to demonstrate this solution works correctly on the testcase above.

https://github.com/llvm/llvm-project/pull/93923