fix: add fchdir

add fchdir and testcases

Change-Id: Idb62087ddc46b3b7db4ceaef478d7b9192115628
Signed-off-by: Nwcc0 <917033401@qq.com>

porting/liteos_a/user/src/stdio/flockfile.c

-#include <unsupported_api.h>
-
-#include "stdio_impl.h"
-#include "pthread_impl.h"
-
-void flockfile(FILE *f)
-{
-	unsupported_api(__FUNCTION__);
-	if (!ftrylockfile(f)) return;
-	__lockfile(f);
-	__register_locked_file(f, __pthread_self());
-}

porting/liteos_a/user/src/unistd/fchdir.c

-#include <unistd.h>
-#include <errno.h>
-#include <fcntl.h>
-#include <unsupported_api.h>
-
-#include "syscall.h"
-
-int fchdir(int fd)
-{
-	unsupported_api(__FUNCTION__);
-	int ret = __syscall(SYS_fchdir, fd);
-	if (ret != -EBADF || __syscall(SYS_fcntl, fd, F_GETFD) < 0)
-		return __syscall_ret(ret);
-
-	char buf[15+3*sizeof(int)];
-	__procfdname(buf, fd);
-	return syscall(SYS_chdir, buf);
-}