[boost] [config] std::uncaught_exceptions

Hello all, std::uncaught_exception (singular) is deprecated in C++17 and will be removed in C++20. std::std::uncaught_exceptions (plural) should be used instead. Will Boost.Config have a macro to detect if std::uncaught_exceptions is supported or not by the current compiler? (For example, Boost.Contract implementation uses std::uncaught_exception and it will need to use std::uncaught_exceptions on C++20 compilers instead.) Thanks. --Lorenzo