cmake dir ‘/xxxxx‘ does not exist after file(MAKE_DIRECTORY)

CMake Error at /usr/local/share/cmake-3.15/Modules/ExternalProject.cmake:1695 (file):
  file problem creating directory: /gtest/src/extern_googletest-stamp
Call Stack (most recent call first):
  /usr/local/share/cmake-3.15/Modules/ExternalProject.cmake:3156 (_ep_set_directories)
  cmake/gtest.cmake:29 (ExternalProject_Add)
  CMakeLists.txt:45 (include)


CMake Error at /usr/local/share/cmake-3.15/Modules/ExternalProject.cmake:1697 (message):
  dir '/gtest/src/extern_googletest-stamp' does not exist after
  file(MAKE_DIRECTORY)
Call Stack (most recent call first):
  /usr/local/share/cmake-3.15/Modules/ExternalProject.cmake:3156 (_ep_set_directories)
  cmake/gtest.cmake:29 (ExternalProject_Add)
  CMakeLists.txt:45 (include)


-- Configuring incomplete, errors occurred!
See also "/mnt/hgfs/main_work/sipproxy_benchmark/build/CMakeFiles/CMakeOutput.log".
See also "/mnt/hgfs/main_work/sipproxy_benchmark/build/CMakeFiles/CMakeError.log".

解决方法：
ExternalProject_Add 模块中 PREFIX 设置错了