slowdown with -std=gnu18 with respect to -std=c99

[Paul Zimmermann]

       Dear Alexander,

> Good point. Also could you please add latency metrics, I see that your testing
> framework already exposes the '--latency' flag.

here are latency metrics (still on i5-4590):

            | gcc-9 | gcc-10 | gcc-11 |
------------|-------|--------|--------|
 -std=c99   | 70.8  | 70.3   | 70.2   |
 -std=gnu18 | 59.5  | 59.5   | 59.5   |

It thus seems the issue only appears for the reciprocal throughput.

Best regards,
Paul