在Ubuntu中安装snappy时，cmake ../时出现以下错误
CMake Error at CMakeLists.txt:294 (add_subdirectory):
The source directory
/home/liuyi/snappy-1.1.9/third_party/googletest
does not contain a CMakeLists.txt file.
CMake Error at CMakeLists.txt:298 (set_property):
set_property could not find TARGET gtest. Perhaps it has not yet been
created.
CMake Error at CMakeLists.txt:300 (set_property):
set_property could not find TARGET gmock. Perhaps it has not yet been
created.
CMake Error at CMakeLists.txt:335 (add_subdirectory):
The source directory
/home/liuyi/snappy-1.1.9/third_party/benchmark
does not contain a CMakeLists.txt file.