CMakeLists.txt: fix googletest related options

[shr-project]

• https://cmake.org/cmake/help/book/mastering-cmake/chapter/Writing%20CMakeLists%20Files.html says that CMake options are case-sensitive and I don't see lower-case version in currently used googletest submodules and gtest is indeed installed with leveldb

• install_gmock option I don't see at all, so I've kept it as is, INSTALL_GTEST, BUILD_GMOCK do exist as upper-case

$ grep -Ri install_.*mock . ./CMakeLists.txt: set(install_gmock OFF) ./third_party/googletest/googlemock/CMakeLists.txt:install_project(gmock gmock_main) $ grep -Ri build_gmock . ./CMakeLists.txt: set(BUILD_GMOCK ON) ./third_party/googletest/googletest/README.md:cmake .. -DBUILD_GMOCK=OFF ./third_party/googletest/CMakeLists.txt:option(BUILD_GMOCK "Builds the googlemock subproject" ON) ./third_party/googletest/CMakeLists.txt:if(BUILD_GMOCK) $ grep -Ri install_gtest . ./CMakeLists.txt: set(INSTALL_GTEST OFF) ./third_party/googletest/googletest/cmake/internal_utils.cmake: if(INSTALL_GTEST) ./third_party/googletest/googletest/CMakeLists.txt:if (INSTALL_GTEST) ./third_party/googletest/CMakeLists.txt:option(INSTALL_GTEST "Enable installation of googletest. (Projects embedding googletest may want to turn this OFF.)" ON)

• also use CACHE and FORCE as sugested in: https://cmake.org/cmake/help/latest/command/set.html https://stackoverflow.com/questions/20239334/cmake-set-subdirectory-options for the value to correctly propagate into third_party/googletest subdirectory

[google-cla[bot]]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.