fixed #4896 (fails to build with MSVC 2013)

fix build error with MSVC 2013 caused by C99 complex support

I already tested in Win8.1 with VS2013 Express 64bit.
Because I am not sure this patch is correct, **please let me know if something is wrong in this patch**.

*How to build(Win8.1+VS2013)*
 - Install VS2013 Express(it support 64bit, don't need Windows SDK)
 - In cmd, execute those commad:
````cmd
cd \path\to\numpy
set VS100COMNTOOLS=%VS120COMNTOOLS%
"C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\vcvarsall.bat" x86_amd64
python setup.py install
````