[release/3.4][Build] Compile FlashAttention on arm64 platforms

[risemeup1111]

PR Category

Environment Adaptation

PR Types

Improvements

Description

1. Remove the NOT WITH_ARM guard from GPU third-party dependency conditions.
2. Allow FlashAttention-related GPU third-party dependency logic to be enabled on ARM64 GPU builds.

Tests

• git diff --check -- cmake/third_party.cmake
• Planned: ARM64 + GPU CMake/build validation with WITH_ARM=ON and WITH_GPU=ON to verify FlashAttention-related third-party dependency logic is enabled on ARM64 GPU builds.

是否引起精度变化

否。本变更仅调整 ARM64 GPU 构建依赖开关，不修改数值计算逻辑或算子实现。

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Cherry-pick of #79488 and #79500 (authored by @liuhao2638) to release/3.4.

devPR:#79488

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