解决printk中的私有函数没有加static的问题

kernel/common/stdio.h

@@ -1,7 +1,13 @@
 #pragma once
+#include <stdarg.h>
+#include <common/printk.h>
 
 #define	SEEK_SET	0	/* Seek relative to start-of-file */
 #define	SEEK_CUR	1	/* Seek relative to current position */
 #define	SEEK_END	2	/* Seek relative to end-of-file */
 
 #define SEEK_MAX	3
+
+extern int vsprintf(char *buf, const char *fmt, va_list args);
+
+extern int sprintk(char *buf, const char *fmt, ...);