Get rid of --with-gtest
It is universally known that to provide a system wide gtest is not the best idea, for instance on macOS homebrew says:
% brew search gtest
Installing gtest system-wide is not recommended; it should be vendored
in your projects that use it.
We have both --with-gtest and --with-gtest-source so one should be removed: clearly --with-gtest should be removed and --with-gtest-source used by all persons wanting unit tests.