[v3] C99 complex math vs. std::complex

[Paolo Carlini]

Benjamin Kosnik wrote:

>Yo dudes. Sorry for the delay.
>
Thanks for the working on this: should fix regressions on many targets!

While you are at it, before I forget: a few days ago I noticed that a 
few 26_numerics/cmath testcases are protected by _GLIBCXX_USE_C99 (and I 
added one ;) Should be changed, more correctly, to just 
_GLIBCXX_USE_C99_MATH?

Paolo.