Configuration - Validate the configuration on CMake 3.10 and later (#762)

Configuration - Validate the configuration on CMake 3.10 and later (#762)

- adm/cmake/gtest.cmake: check CMake version before using FetchContent; emit a warning and skip FetchContent-based GoogleTest setup when CMake < 3.11.
- adm/cmake/occt_macros.cmake: wrap list(REMOVE_DUPLICATES ...) calls in if() checks to avoid operating on empty/unset variables.