[newlib] Remove compiling warning.

Author: BernardXiong

components/libc/newlib/syscalls.c

@@ -3,6 +3,14 @@
 #include <sys/time.h>
 #include <rtthread.h>
 
+#ifdef RT_USING_DFS
+#include <dfs_posix.h>
+#endif
+
+#ifdef RT_USING_PTHREADS 
+#include <pthread.h>
+#endif
+
 /* Reentrant versions of system calls.  */
 
 int