utils/os_socket: Define ssize_t on windows.

Fixes: ef5266ebd5 ("util/os_socket: Add socket related functions.")

Reviewed-by: Roland Scheidegger <sroland@vmware.com>

src/util/os_socket.h

@@ -10,6 +10,10 @@
 
 #include <stdio.h>
 #include <stdbool.h>
+#ifdef _MSC_VER
+#include <BaseTsd.h>
+typedef SSIZE_T ssize_t;
+#endif
 
 #ifdef __cplusplus
 extern "C" {