[clang] Fix printing of templated records. (PR #86339)

[Zahira Ammarguellat via cfe-commits]

zahiraam wrote:

> I'm getting errors like:
> 
> ```
> llvm-project/clang/unittests/AST/DeclPrinterTest.cpp:1394:3: error: expression result unused [-Werror,-Wunused-value]
>   [](PrintingPolicy &Policy) { Policy.SuppressTagKeyword = false; };
> ```
> 
> This file being a clang test, I am wondering if this is actually part of the test. Shall we put `[[maybe_unused]]` here?

@kazutakahirata  When do you get this error? 

https://github.com/llvm/llvm-project/pull/86339