Add xplat cxx_binary target for bench_sdpa #29837

Job	Run time
gather-models	8s
test-models-linux (buck2, mv3, xnnpack-quantization-delegation, linux.2xlarge, 90) / linux-job	3m 40s
test-models-linux (cmake, vit, xnnpack-quantization-delegation, linux.2xlarge, 90) / linux-job	3m 40s
test-models-linux (cmake, mv3, xnnpack-quantization-delegation, linux.2xlarge, 90) / linux-job	3m 40s
test-models-linux (cmake, mv3, portable, linux.2xlarge, 90) / linux-job	3m 40s
test-models-linux (cmake, vit, portable, linux.2xlarge, 90) / linux-job	1s
test-models-linux (buck2, mv3, portable, linux.2xlarge, 90) / linux-job	1s
	14m 50s

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