[clang] [clang][dataflow] Bail out if input is Objective-C++. (PR #86479)

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llvmbot wrote:

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>/cherry-pick https://github.com/llvm/llvm-project/commit/e6f63a942a45e3545332cd9a43982a69a4d5667b

Error: Command failed due to missing milestone.

https://github.com/llvm/llvm-project/pull/86479