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.h

@@ -30,10 +30,8 @@ typedef struct host_t host_t;
 #include <stdlib.h>
 #include <stdio.h>
 #include <sys/types.h>
-#include <sys/socket.h>
-#include <netinet/in.h>
-#include <arpa/inet.h>
 
+#include <utils/utils.h>
 #include <utils/chunk.h>
 
 /**

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"