message: GTest: workaround option cache overwriting
diff: -set(BUILD_GTEST ON)
  -set(BUILD_GMOCK OFF)
  +set(BUILD_GTEST ON CACHE INTERNAL "")
  +set(BUILD_GMOCK OFF CACHE INTERNAL "")
  set(gtest_disable_pthreads ON)
  set(CMAKE_POLICY_DEFAULT_CMP0042 NEW)
  