message: Fix linking errors with CMake 3.12
diff: @@ -5,6 +5,9 @@ set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
  set(INSTALL_GMOCK OFF CACHE BOOL "" FORCE)
  set(INSTALL_GTEST OFF CACHE BOOL "" FORCE)
  +# Work around the linking errors when compiling gtest with CUDA
  +set(gtest_disable_pthreads ON CACHE BOOL "" FORCE)
  +
  load_git_package(gtest
  "https://github.com/google/googletest.git"
  "d5266326752f0a1dadbd310932d8f4fd8c3c5e7d")
  