注意要用正斜杠  /    不要用 \

https://github.com/opencv/opencv/issues/11655

CMake Error at cmake/OpenCVModule.cmake:368 (_glob_locations):
  Syntax error in cmake code at

    E:/opencv_github/opencv/cmake/OpenCVModule.cmake:368

  when parsing string

    E:\opencv_github\opencv_contrib\modules

  Invalid character escape ‘\o‘.
Call Stack (most recent call first):
  modules/CMakeLists.txt:7 (ocv_glob_modules)


而且很多时候连接都不好，需要自己下载文件
https://www.cnblogs.com/huluwa508/p/10142718.html

windows编译opencv_contrib的小坑