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

[via cfe-commits]

github-actions[bot] wrote:

<!--LLVM CODE FORMAT COMMENT: {clang-format}-->

:white_check_mark: With the latest revision this PR passed the C/C++ code formatter.

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