usrsctp does not build with mingw

```
usrsctp does not build with mingw.  Various errors including "sys/socket.h" 
appear during build.  If -D__Userspace_os_Windows is set as a Cflag it will not 
build due to differences between GCC and MSVC. Mingw should be a supported 
compiler.


```

Original issue reported on code.google.com by `JohnWas...@gmail.com` on 15 May 2015 at 10:32
