fix opendir, fpathconf and ttyname_r to use fstat64(), not fstat()

fix opendir, fpathconf and ttyname_r to use fstat64(), not fstat()

There is no opendir64(), thus even programs built for 64-bit off_t
use opendir(). Before this change, internally opendir() uses fstat(),
with the following breakage if some of struct stat fields are too narrow:

$ strace ls -l
execve("/busybox/ls", ["ls", "-l"], 0x7ffcdc43ede8 /* 16 vars */) = 0
ioctl(0, TCGETS, {B38400 opost isig icanon echo ...}) = 0
ioctl(1, TCGETS, {B38400 opost isig icanon echo ...}) = 0
getuid32()                              = 0
time([1551486393 /* 2019-03-02T00:26:33+0000 */]) = 1551486393 (2019-03-02T00:26:33+0000)
ioctl(0, TIOCGWINSZ, {ws_row=38, ws_col=120, ws_xpixel=0, ws_ypixel=0}) = 0
ioctl(1, TCGETS, {B38400 opost isig icanon echo ...}) = 0
brk(NULL)                               = 0x9768000
brk(0x9769000)                          = 0x9769000
lstat64(".", 0xffa6e374)                = 0
open(".", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_DIRECTORY) = 3
fstat(3, 0xffa6e378)                    = -1 EOVERFLOW (Value too large for defined data type)

See https://bugs.busybox.net/show_bug.cgi?id=11651

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>