* sysdeps/unix/sysv/linux/internal_statvfs64.c: New file.
* sysdeps/unix/sysv/linux/Makefile [subdir=io] (sysdep_routines):
Add internal_statvfs64.
* sysdeps/unix/sysv/linux/internal_statvfs.c: Allow to be used to
compile 64bit version.
* sysdeps/unix/sysv/linux/statvfs64.c: Use __fstatfs64 and skip
compatibility code if __ASSUME_STATFS64 is defined.
* sysdeps/unix/sysv/linux/fstatvfs64.c: Likewise.
* sysdeps/unix/sysv/linux/statfs64.c: Don't add __no_statfs64 if
__ASSUME_STATFS64 != 0.