Fix Windows ARM64 build failure from x86-only memory fence

[Copilot]

The build (windows-11-arm, arm64, windows-arm64, windows) job failed because the Windows build path used an x86-only fence intrinsic in shared code. On ARM64 runners, MSVC could not resolve _mm_mfence, stopping compilation of PretextView.cpp.

• Root cause

  • ThreadFence in include/Header.h mapped to _mm_mfence() for all Windows targets.
  • That intrinsic is not available on Windows ARM64, even though the same header is used by the ARM64 build.

• Change

  • Replaced the Windows ThreadFence definition with MemoryBarrier().
  • This preserves the intended full memory barrier semantics while removing the x86-specific dependency from the Windows code path.

• Impact

  • Unblocks compilation on Windows ARM64 runners.
  • Keeps existing non-Windows behavior unchanged.

• Relevant snippet

  #ifndef _WIN32
  #define ThreadFence __asm__ volatile("" ::: "memory")
  #else
  #define ThreadFence MemoryBarrier()
  #endif // _WIN32