FindCUDAToolkit.cmake must support cross-compiling

Most recent FindCUDAToolkit.cmake on master (last change: 6e474364) can't find cuda tk headers and libraries when cmake is cross-compiling. The logic is present in FindCUDA.cmake but wasn't ported to the new module.

From my tests, it suffices to add the following just before the libs and headers are found:

if(CMAKE_CROSSCOMPILING)
  if(CMAKE_SYSTEM_PROCESSOR STREQUAL "armv7-a")
    # Support for NVPACK
    set (CUDAToolkit_TARGET_NAME "armv7-linux-androideabi")
  elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "arm")
    # Support for arm cross compilation
    set(CUDAToolkit_TARGET_NAME "armv7-linux-gnueabihf")
  elseif(CMAKE_SYSTEM_PROCESSOR MATCHES "aarch64")
    # Support for aarch64 cross compilation
    if (ANDROID_ARCH_NAME STREQUAL "arm64")
      set(CUDAToolkit_TARGET_NAME "aarch64-linux-androideabi")
    else()
      set(CUDAToolkit_TARGET_NAME "aarch64-linux")
    endif (ANDROID_ARCH_NAME STREQUAL "arm64")
  endif()

  if (EXISTS "${CUDAToolkit_ROOT_DIR}/targets/${CUDAToolkit_TARGET_NAME}")
    set(CUDAToolkit_TARGET_DIR "${CUDAToolkit_ROOT_DIR}/targets/${CUDAToolkit_TARGET_NAME}" CACHE PATH "CUDA Toolkit target location.")    
    mark_as_advanced(CUDAToolkit_TARGET_DIR)
  endif()

  # add known CUDA target root path to the set of directories we search for programs, libraries and headers
  set(CMAKE_FIND_ROOT_PATH "${CUDAToolkit_TARGET_DIR};${CMAKE_FIND_ROOT_PATH}")
else()
  set(CUDAToolkit_TARGET_DIR ${CUDAToolkit_ROOT_DIR})
endif()