[llvm] [X86] Avoid invalid ret for EH_RETURN with SHSTK (PR #219322)

[via llvm-commits]

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linisha15 wrote:

Added nounwind. This also dropped the .seh_* epilogue directives from the WIN64/WINRET blocks (same unwind-info category as .cfi_*), so those check blocks got shorter too. All RUN lines pass.

https://github.com/llvm/llvm-project/pull/219322