ITS#8383 Look for socklen_t in <ws2tcpip.h> too

MinGW targets do not have the <sys/socket.h> header. The configure check
would conclude that there is no socklen_t type, resulting in portable.h
containing its own definition of socklen_t, which would later conflict
with the actual definition in <ws2tcpip.h>.

Add <ws2tcpip.h> to the configure check for socklen_t, so that the
defined type is correctly detected.

configure.in

@@ -2259,6 +2259,9 @@ AC_CHECK_TYPES([ptrdiff_t])
 AC_CHECK_TYPE([socklen_t],,, [$ac_includes_default
 #ifdef HAVE_SYS_SOCKET_H
 #include <sys/socket.h>
+#endif
+#ifdef HAVE_WINSOCK2
+#include <ws2tcpip.h>
 #endif])
 
 dnl socklen_t-like type in accept(), default socklen_t or int: