[libc] Update libc.

1. Add POSIX termios implementation;
2. Add POSIX signals implementation;
3. Add stdio for each libc.

components/libc/compilers/dlib/stdio.c

@@ -0,0 +1,70 @@
+/*
+ * File     : stdio.c
+ * Brief    : stdio/console
+ *
+ * This file is part of RT-Thread RTOS
+ * COPYRIGHT (C) 2006 - 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
+ * 2017/10/15     bernard      implement stdio for IAR dlib.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <rtthread.h>
+#include "libc.h"
+
+#if defined(RT_USING_DFS) && defined(RT_USING_DFS_DEVFS)
+#include <dfs_posix.h>
+
+#define STDIO_DEVICE_NAME_MAX   32
+
+static int std_fd = -1;
+int libc_stdio_set_console(const char* device_name, int mode)
+{
+    int fd;
+    char name[STDIO_DEVICE_NAME_MAX];
+
+    snprintf(name, sizeof(name) - 1, "/dev/%s", device_name);
+    name[STDIO_DEVICE_NAME_MAX - 1] = '\0';
+
+    fd = open(name, mode, 0);
+    if (fd >= 0)
+    {
+        if (std_fd >= 0)
+        {
+            close(std_fd);
+        }
+        std_fd = fd;
+    }
+
+    return std_fd;
+}
+
+int libc_stdio_read(void *buffer, size_t size)
+{
+    return read(std_fd, buffer, size);
+}
+
+int libc_stdio_write(const void *buffer, size_t size)
+{
+    return write(std_fd, buffer, size);
+}
+#endif