Added preprocessor directives around errno

src/include/lwip/errno.h

@@ -174,7 +174,12 @@ extern "C" {
 #define  EMEDIUMTYPE    124  /* Wrong medium type */
 
 #ifndef errno
-extern int errno;
+//extern int errno;
+#if defined(__linux__) && !defined(__ANDROID__)
+	#include <errno.h>
+#else
+	extern int errno;
+#endif
 #endif
 
 #else /* LWIP_PROVIDE_ERRNO */