[posix][libc] 优化libc中posix结构

components/libc/compilers/gcc/newlib/stdio.c

@@ -7,16 +7,16 @@
  * Date           Author       Notes
  * 2017/10/15     bernard      the first version
  */
+#include <rtthread.h>
+
+#ifdef RT_LIBC_USING_FILEIO
 #include <stdio.h>
 #include <stdlib.h>
 #include <fcntl.h>
-#include <rtthread.h>
 #include "libc.h"
 
 #define STDIO_DEVICE_NAME_MAX   32
 
-int _EXFUN(fileno, (FILE *));
-
 static FILE* std_console = NULL;
 
 int libc_stdio_set_console(const char* device_name, int mode)
@@ -79,3 +79,5 @@ int libc_stdio_get_console(void)
     else
         return -1;
 }
+
+#endif /* RT_LIBC_USING_FILEIO */