Merge pull request #1854 from RT-Thread/fix_libc_EXFUN

[libc] Add _EXFUN judgement

components/libc/compilers/newlib/libc.h

@@ -26,8 +26,15 @@
 #ifndef __RTT_LIBC_H__
 #define __RTT_LIBC_H__
 
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
 #include <sys/time.h>
 
+#ifndef _EXFUN
+#define _EXFUN(name, proto)		name proto
+#endif
+
 #define MILLISECOND_PER_SECOND  1000UL
 #define MICROSECOND_PER_SECOND  1000000UL
 #define NANOSECOND_PER_SECOND   1000000000UL