windows: Add a common Windows header for platform specific wrappers

Include some more basic system headers in utils.h, so we can use that common
header on the different platforms.

src/libstrongswan/networking/host_resolver.c

@@ -14,8 +14,6 @@
  */
 
 #include <sys/types.h>
-#include <sys/socket.h>
-#include <netdb.h>
 
 #include "host_resolver.h"