arch/x64: Fix crash issue after enabling KASAN

[xianglyc]

After up_fork calls the x86_64_fork function, the rsp must be 16-byte aligned; otherwise, the movaps %xmm0, (%rsp) instruction may cause a crash.

Note: Please adhere to Contributing Guidelines.

Summary

After up_fork calls the x86_64_fork function, the rsp must be 16-byte aligned; otherwise, the movaps %xmm0, (%rsp) instruction may cause a crash.

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Impact

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Testing

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