just to be clear about the abi issues mentioned here, neither c++ nor c have a standardised abi. but there are widely agreed abis for different platforms. standardised language changes can thus not break standardised abis, because the standards don't specify abis.
WG21 can, and has in the past[0], broken platforms' ABIs. It tends to be painful enough that platform vendors (who are represented on the committees) aren't interested in doing it again.
