add sleep/usleep/useconds_t to unistd.h

Author: ZERICO2005

src/libc/include/unistd.h

@@ -3,6 +3,13 @@
 
 #include <cdefs.h>
 
+/*
+ * unsigned int sleep(unsigned int seconds);
+ * typedef unsigned int useconds_t;
+ * int usleep(useconds_t usec);
+ */
+#include <sys/timers.h>
+
 #define STDIN_FILENO 0
 #define STDOUT_FILENO 1
 #define STDERR_FILENO 2