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

[Stephan T. Lavavej via cfe-commits]

StephanTLavavej wrote:

MSVC always uses 64-bit `long double`. I don't know anything about attempts to use 80-bit `long double` on Windows except that they're asking for tons of complexity.

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