win32: Add define for missing EPROTONOSUPPORT

mingw32 does not define EPROTONOSUPPORT (which is used by
migration.c and maybe future patches), so add a
definition which uses a supported errno value.
Signed-off-by: NStefan Weil <weil@mail.berlios.de>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

qemu-os-win32.h

@@ -49,4 +49,8 @@ static inline void os_setup_post(void) {}
 static inline void os_set_line_buffering(void) {}
 static inline void os_set_proc_name(const char *dummy) {}
 
+#if !defined(EPROTONOSUPPORT)
+# define EPROTONOSUPPORT EINVAL
+#endif
+
 #endif