Check Error with libstdc++

[B. Kosnik]

> FAIL: 26_numerics/c99_classification_macros_c.cc (test for excess
> errors)
> 
>                 === libstdc++-v3 Summary ===
> 
> # of expected passes            397
> # of unexpected failures        1
> # of unexpected successes       10
> # of expected failures          16

Known failure for this platform. Don't worry about it.

-benjamin