[clang] [clang][AST] fix ast-print of `extern <lang>` with >=2 declarators (PR #93131)

[Artem Yurchenko via cfe-commits]

temyurchenko wrote:

> No worries, and I reverted it for you. When you have the fix ready, I'm happy to verify it on our builders before you reland.

Can you also reopen this PR, please? For documentation/history reasons, it's probably better to provide a fix within the scope of this PR.

https://github.com/llvm/llvm-project/pull/93131