HeCBench

[tsne-sycl] add the category and reference for the examples

[tsne-sycl] set the GCC_TOOLCHAIN option properly if needed

[tsne-sycl] add the C++ complex header

[tsne] add the text file from Velocity-Bench (https://github.com/zjin-lcf/HeCBench/issues/106)

[opticalFlow] add the input files from CUDA samples (https://github.com/zjin-lcf/HeCBench/issues/106); the input files are specified as command-line arguments