[PATCH v3 3/7] Assume support for __extension__ ({ })

[Florian Weimer]

* Bruno Haible:

>> -  restrict
>
> Beware! Present by default in gcc >= 5.x only.
> Only if spelled as __restrict__, it is present in gcc >= 2.95.3 at least.

It's also not in C++.

Thanks,
Florian