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

[Artem Yurchenko via cfe-commits]

temyurchenko wrote:

> We started seeing an lldb test failure, and I bisected to this commit:

I see the source of the bug, I'm thinking how to address it best. If it's urgent, I can produce an urgent fix.

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