lwip: Fix compatibility issues with later versions

The name of the header guard in lwIP's <lwip/opt.h> has changed from
'__LWIP_OPT_H__' to 'LWIP_HDR_OPT_H' (bug #35874 in May 2015).

Other fixes:

- In curl_setup.h, the problem with an old PSDK doesn't apply if lwIP is
used.

- In memdebug.h, the 'socket' should be undefined first due to lwIP's
lwip_socket() macro.

- In curl_addrinfo.c lwIP's getaddrinfo() + freeaddrinfo() macros need
special handling because they were undef'ed in memdebug.h.

- In select.c we can't use preprocessor conditionals inside select if
MSVC and select is a macro, as it is with lwIP.

http://curl.haxx.se/mail/lib-2015-12/0023.html
http://curl.haxx.se/mail/lib-2015-12/0024.html

lib/curl_setup.h

@@ -481,9 +481,10 @@
 /*
  * msvc 6.0 requires PSDK in order to have INET6_ADDRSTRLEN
  * defined in ws2tcpip.h as well as to provide IPv6 support.
+ * Does not apply if lwIP is used.
  */
 
-#if defined(_MSC_VER) && !defined(__POCC__)
+#if defined(_MSC_VER) && !defined(__POCC__) && !defined(USE_LWIPSOCK)
 #  if !defined(HAVE_WS2TCPIP_H) || \
      ((_MSC_VER < 1300) && !defined(INET6_ADDRSTRLEN))
 #    undef HAVE_GETADDRINFO_THREADSAFE
@@ -675,7 +676,7 @@ int netware_init(void);
  * Ensure that Winsock and lwIP TCP/IP stacks are not mixed.
  */
 
-#if defined(__LWIP_OPT_H__)
+#if defined(__LWIP_OPT_H__) || defined(LWIP_HDR_OPT_H)
 #  if defined(SOCKET) || \
      defined(USE_WINSOCK) || \
      defined(HAVE_WINSOCK_H) || \