[Bug libstdc++/89991] Complex numbers: Calculation of imaginary part is not correct

[kargl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89991

--- Comment #23 from kargl at gcc dot gnu.org ---
Created attachment 46105
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46105&action=edit
fix g++ problem with pow(z,0.5) where imag(z) = -0.

This patch has only been tested with the original test provided by the
reporter.