[Kernel] header files

1. Remove components.h file;
2. Add libc_* files for standard libc definitions;
3. Add rtdbg.h file for simple debug log;
4. Add single list implementation;
5. Change the 'rt_uint8_t' type of cmd to 'int'.

include/rtlibc.h

@@ -0,0 +1,42 @@
+/*
+ * File      : rtlibc.h
+ * This file is part of RT-Thread RTOS
+ * COPYRIGHT (C) 2017, RT-Thread Development Team
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License along
+ *  with this program; if not, write to the Free Software Foundation, Inc.,
+ *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Change Logs:
+ * Date           Author       Notes
+ * 2017-01-21     Bernard      the first version
+ */
+
+#ifndef RTLIBC_H__
+#define RTLIBC_H__
+
+/* definitions for libc if toolchain has no these definitions */
+#include "libc/libc_stat.h"
+#include "libc/libc_errno.h"
+
+#include "libc/libc_fcntl.h"
+#include "libc/libc_ioctl.h"
+#include "libc/libc_dirent.h"
+#include "libc/libc_signal.h"
+
+#if defined(__CC_ARM) || defined(__IAR_SYSTEMS_ICC__)
+typedef signed long off_t;
+#endif
+
+#endif
+