* dirent/Makefile (routines): Add getdents64.
* sysdeps/unix/sysv/linux/Makefile [dirent] (sysdep_routines):
Remove getdents64.
* dirent/dirent.h: Redirect getdirentries to getdirentries64 if
compiled with _FILE_OFFSET_BITS=64.
* sysdeps/generic/getdents64.c: New file.
* sysdeps/unix/sysv/linux/getdirentries.c: Also redefine off_t and
__lseek for getdirentries64 definition.
* sysdeps/unix/sysv/linux/llseek.c: Make __lseek64 a strong alias.
* sysdeps/unix/sysv/linux/sys/sendfile.h: Don't allow use with
_FILE_OFFSET_BITS=64.
