[clang] [Clang][Windows] Preserve x86_fp80 and vector alignment under #pragma pack. (PR #208256)

[Oliver Hunt via cfe-commits]

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+// RUN: %clang_cc1 -triple x86_64-pc-windows-msvc -emit-llvm -o - %s \
+// RUN: | FileCheck %s
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ojhunt wrote:

(existing tests I mean, not "does this PR have them")

https://github.com/llvm/llvm-project/pull/208256