Can‘t find third_party/gtest. Run git submodule update --init, or disable with CMake -DBUILD_TEST

使用cmake编译时的一个错误。详细来说：

CMake Error at CMakeLists.txt:565 (message):
  Can't find third_party/gtest.  Run git submodule update --init, or disable
  with CMake -DBUILD_TESTS=OFF.

 解决办法

cmake .. -DBUILD_TESTS=OFF