include: Add stuff related to WSAPoll() (try 3)

[Sebastian Lackner]

On 17.07.2015 18:29, Bruno Jesus wrote:
> Try to apply Matteo's idea to not redefine the struct when port.h was
> already included. I can't test in mingw myself unfortunately.

I don't think this will work properly. The Linux pollfd struct contains "fd" with
type "int", but on Windows its defined as "SOCKET" (which has size of a pointer).
My personal preference would be to just leave out the "struct pollfd" definition
here, and only declare WSAPOLLFD. Basically:

+typedef struct
+{
+    SOCKET fd;
+    SHORT events;
+    SHORT revents;
+} WSAPOLLFD;

Not sure if this would be an acceptable solution for the other devs though.