A number of minor fixes to build on MacOS

• project(Gaudi) is just to avoid a warning
• Forward declaration of std::chrono::duration produces a compilation error: error: reference to 'chrono' is ambiguous
• std::tuple of a literal string produces the following error: no viable constructor or deduction guide for deduction of template arguments of 'tuple' auto t = std::tuple{500, 1.0, "sec"};
• The Apple clang version starts with a two digit number.