bug#80106: Don't sort dirents (in du) for Lustre

>> For context, Lustre is an open-source (GPLv2) out-of-tree Linux filesystem
>> commonly used for HPC applications.
>>
>> Let me know if you need anymore context. Thanks!
>
>Could you check coreutils built with this patch and see if it fixes the
>performance? I can push it to Gnulib afterwards:

Works perfectly:

$ echo 3 | sudo tee /proc/sys/vm/drop_caches 
3
$ time coreutils-9.9-unpatched/src/du /fsx/test_100K > /dev/null

real	1m54.268s
user	0m0.229s
sys	0m14.136s
$ echo 3 | sudo tee /proc/sys/vm/drop_caches 
3
$ time coreutils-9.9-patched/src/du /fsx/test_100K > /dev/null

real	0m13.150s
user	0m0.075s
sys	0m1.956s

That's around a 9x speedup. I haven't tested any other commands.
Lustre statahead (which is giving the performance boost) is designed
for "stat everything in a directory" type workloads. The other commands
wouldn't do that, I think. Perhaps chown would? Either way, thanks for
the help!

Tim Day