Update FREERTOS + LWIP support

mongoose.h

@@ -192,10 +192,10 @@ extern "C" {
 
 #if MG_ARCH == MG_ARCH_FREERTOS_LWIP
 
-#include <errno.h>
 #include <stdarg.h>
 #include <stdbool.h>
 #include <stdint.h>
+#include <string.h>
 
 #if defined(__GNUC__)
 #include <sys/stat.h>
@@ -213,6 +213,17 @@ struct timeval {
 
 #include <lwip/sockets.h>
 
+#if LWIP_SOCKET != 1
+// Sockets support disabled in LWIP by default 
+#error Set LWIP_SOCKET variable to 1 (in lwipopts.h)
+#endif
+
+#if LWIP_POSIX_SOCKETS_IO_NAMES != 0
+// LWIP_POSIX_SOCKETS_IO_NAMES must be disabled in posix-compatible OS enviroment
+// (freertos mimics to one) otherwise names like `read` and `write` conflict
+#error LWIP_POSIX_SOCKETS_IO_NAMES must be set to 0 (in lwipopts.h) for FreeRTOS
+#endif
+
 #define MG_INT64_FMT "%lld"
 #define MG_DIRSEP '/'