Method CerrStream

extras/catch_amalgamated.cpp:4632–4632

Store the streambuf from cerr up-front because cout may get redirected when running tests

            // Store the streambuf from cerr up-front because
            // cout may get redirected when running tests
            CerrStream(): m_os( Catch::cerr().rdbuf() ) {}

        public: // IStream
            std::ostream& stream() override { return m_os; }