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

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

I think we're going to be printing incorrect code either way, but with this patch, we're more likely to be closer to the original intent of the code than without the patch. So even though this isn't perfect, it's forward progress and I think we're fine to land it as-is. However, if we can fix it correctly, that would be preferred.

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