Switch to modern CMake CUDA handling (apache#17031)

Introduce unified MXNET_CUDA_ARCH option to specify cuda architectures.
Previously cuda architecture setting was partially broken and different options
were applied to different parts of the build (CUDA_ARCH_NAME CUDA_ARCH_BIN
CUDA_ARCH_PTX and CUDA_ARCH_LIST).
Include FindCUDAToolkit from CMake 3.17, which replaces the deprecated FindCUDA
functionality for finding the cuda toolkit include directories and libraries.

Workaround for DLL size limitation on Windows (apache#16980)
* change windows build system.
add gen_warp cpp version
add add_custom_command to run warp_gen
add download cmake
add option
change option
add dynamic read mxnet dll