[swift-evolution] #if os(Windows) and MSVC/Cygwin Compatibility

[Joe Groff]

> On May 3, 2016, at 9:27 PM, Chris Lattner via swift-evolution <swift-evolution at swift.org> wrote:
> 
> MSVC and MinGW (again, AFAIK) use the same C ABI, and thus could be treated as the same target.
> 
Part of the problem is that MSVC and Mingw *don't* share a C ABI or runtime. Only 'stdcall' and COM stuff from the Win32 system APIs is portable between them at the binary level. 

-Joe