Get cygwin compilation working

These are the basic changes I needed to make to get cygwin support up to the python module compiling and loading.

The test exe doesn't link though because of missing `__declspec(dllexport)` across the YouCompleteMe namespace function declarations. I wasn't sure which way you'd like to do this, or if you even cared if tests ran on cygwin/windows.

I also think [this line](https://github.com/cehoffman/YouCompleteMe/pull/new/cygwin_support#L1L220) probably needs `WIN32` in it but I don't have that setup, so I didn't add it.