Fix lwip2 ping (esp8266#8596)

fixes esp8266#8555
related to dancol90/ESP8266Ping#42

Author: d-a-v

tools/sdk/lib/liblwip2-1460-feat.a

@@ -1,5 +1,5 @@
 // generated by makefiles/make-lwip2-hash
 #ifndef LWIP_HASH_H
 #define LWIP_HASH_H
-#define LWIP_HASH_STR "STABLE-2_1_3_RELEASE/glue:1.2-61-g679577b"
+#define LWIP_HASH_STR "STABLE-2_1_3_RELEASE/glue:1.2-63-gb5def38"
 #endif // LWIP_HASH_H

tools/sdk/lib/liblwip2-1460.a

@@ -190,7 +190,7 @@ typedef uintptr_t mem_ptr_t;
  * sys/types or unistd.h are available).
  * Being like that, we define it to 'int' if SSIZE_MAX is not defined.
  */
-#if !defined(SSIZE_MAX) || !defined(_SSIZE_T_DECLARED)
+#ifdef SSIZE_MAX
 /* If SSIZE_MAX is defined, unistd.h should provide the type as well */
 #ifndef LWIP_NO_UNISTD_H
 #define LWIP_NO_UNISTD_H 0