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

[via cfe-commits]

gulfemsavrun wrote:

We started seeing an lldb test failure, and I bisected to this commit:
```
--
Command Output (stderr):
--
FAIL: LLDB (/b/s/w/ir/x/w/llvm_build/bin/clang-x86_64) :: test_completions (TestDAP_completions.TestDAP_completions.test_completions)
FAIL: LLDB (/b/s/w/ir/x/w/llvm_build/bin/clang-x86_64) :: test_completions (TestDAP_completions.TestDAP_completions.test_completions)
======================================================================
ERROR: test_completions (TestDAP_completions.TestDAP_completions.test_completions)
   Tests the completion request at different breakpoints
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/b/s/w/ir/x/w/llvm-llvm-project/lldb/packages/Python/lldbsuite/test/decorators.py", line 150, in wrapper
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/b/s/w/ir/x/w/llvm-llvm-project/lldb/test/API/tools/lldb-dap/completions/TestDAP_completions.py", line 89, in test_completions
    self.dap_server.get_completions("`log enable  "),
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/b/s/w/ir/x/w/llvm-llvm-project/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py", line 448, in get_completions
    response = self.request_completions(text, frameId)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/b/s/w/ir/x/w/llvm-llvm-project/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py", line 979, in request_completions
    return self.send_recv(command_dict)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/b/s/w/ir/x/w/llvm-llvm-project/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py", line 324, in send_recv
    raise ValueError(desc)
ValueError: no response for "completions"
Config=x86_64-/b/s/w/ir/x/w/llvm_build/bin/clang
======================================================================
ERROR: test_completions (TestDAP_completions.TestDAP_completions.test_completions)
   Tests the completion request at different breakpoints
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/b/s/w/ir/x/w/llvm-llvm-project/lldb/packages/Python/lldbsuite/test/lldbtest.py", line 2017, in tearDown
    Base.tearDown(self)
  File "/b/s/w/ir/x/w/llvm-llvm-project/lldb/packages/Python/lldbsuite/test/lldbtest.py", line 1103, in tearDown
    hook()  # try the plain call and hope it works
    ^^^^^^
  File "/b/s/w/ir/x/w/llvm-llvm-project/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/lldbdap_testcase.py", line 375, in cleanup
    self.dap_server.request_disconnect(terminateDebuggee=True)
  File "/b/s/w/ir/x/w/llvm-llvm-project/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py", line 666, in request_disconnect
    return self.send_recv(command_dict)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/b/s/w/ir/x/w/llvm-llvm-project/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py", line 318, in send_recv
    self.send_packet(command)
  File "/b/s/w/ir/x/w/llvm-llvm-project/lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py", line 273, in send_packet
    self.send.flush()
BrokenPipeError: [Errno 32] Broken pipe
Config=x86_64-/b/s/w/ir/x/w/llvm_build/bin/clang
----------------------------------------------------------------------
Ran 1 test in 1.600s

FAILED (errors=2)

--
```
https://logs.chromium.org/logs/fuchsia/buildbucket/cr-buildbucket/8746482644341901905/+/u/lldb/test/stdout

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