Due to the small flash space on AVR devices the library containing the
standard types in C++ (ˋlibstdc++ˋ) does not get built normally when
enabling the C++ language support.
This option is an easy way to go back to the PC-way where ˋlibstdc++ˋ is
built.
Signed-off-by: Quentin Boswank <qubos@outlook.de>