VS: Set CUDA TargetMachinePlatform explicitly on x64

Brad Kingrequested to merge
brad.king/cmake:vs-cuda-machine into master

The TargetMachinePlatform setting tells CUDA what --machine {32,64} flag to pass to nvcc. While CUDA automatically chooses the proper default for the target architecture, it does not reflect this in the user-visible IDE settings. Set it explicitly to fix the user-visible setting.

Fixes: #17355 (closed)

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