[bsp][lm3s8962] Fix complie error. Add missing macro RT_USING_LIBC. Force use Lwip 1.4.1 bye define RT_USING_LWIP141

bsp/lm3s8962/rtconfig.h

@@ -153,4 +153,6 @@
 /* the size of each pbuf in the pbuf pool. */
 #define RT_LWIP_PBUF_POOL_BUFSIZE		1500
 
+#define RT_USING_LIBC
+#define RT_USING_LWIP141
 #endif