If you were to write a program that relies on those aspects of the abstract C machine and don't provide those aspects, then you might have an argument, in that in that case the observable behaviour would be different, but if you choose not to make use of that functionality, its presence is entirely irrelevant.

This is also massively shifting goal posts. You first wrote "At which point it is no longer C". By your argument here, e.g. the Linux kernel is not written predominantly in C. But nobody uses the term that way. If you were to speak specifically about ISO C, maybe, but the person I replied to initially did not limit it to ISO C.

As such this is also entirely irrelevant to the original argument.