[clang] [X86_64] fix SSE type error in vaarg. (PR #86377)

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llvmbot wrote:

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>/cherry-pick https://github.com/llvm/llvm-project/commit/9c8dd5e6f6bd93deb95de9642632223f54a18a11

Error: Command failed due to missing milestone.

https://github.com/llvm/llvm-project/pull/86377