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

[Kazu Hirata via cfe-commits]

kazutakahirata 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?

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