libstdcxx-dual-abi needs to be enabled to actually support C++11 ABI.
Enable the config flag to also permit support of .NET 6 development on
OpenWrt.
Signed-off-by: Ivan Maslov <avenger_msoft@mail.ru>
[ reword commit description and title ]
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>