misoptimization causing der_io.f90 failures

[Tobias Schlüter]

Joe Buck wrote:
>>Should I file a PR? It didn't seem to be the right thing, as the 
>>testsuite keeps reminding us of that failure anyway.
> 
> 
> Yes, please file a PR, it makes things like this easier to track.
> The PR should contain your analysis so far, or a pointer to your
> previous gcc list message.

This is now PR15449.

Regards,
- Tobi