Allow repeated flags much more often

Nobody has claimed this yet.

If seems that there are many cases where we define self-conflicts, but GNU accepts repeated arguments. This is especially unnecessary for boolean flags. Let's fix that! This issue tracks progress for all utils.

chgrp: at least -v is broken
chmod: not considered yet
chown: not considered yet
chroot: not considered yet
comm: at least -1 is broken
cp: at least -a is handled correctly
csplit: at least -k is broken
date: at least --resolution is broken: #6143 , rest is fixed by #6142
du: at least -s is broken
echo: at least -n is broken
fmt: at least -c is broken, fixed by #6355
fold: at least -b is broken
id: at least -u is broken
install: at least -b is broken
join: at least -z is broken
kill: at least -l is broken
ln: not considered yet
logname: not considered yet
ls: not considered yet
mkdir: not considered yet
mkfifo: not considered yet
mknod: not considered yet
mktemp: not considered yet
more: not considered yet
mv: not considered yet
nice: not considered yet
nl: not considered yet
nohup: not considered yet
nproc: not considered yet
numfmt: not considered yet
od: not considered yet
paste: not considered yet
pathchk: not considered yet
pinky: not considered yet
pr: not considered yet
printenv: not considered yet
printf: not considered yet
ptx: not considered yet
pwd: not considered yet
readlink: not considered yet
realpath: not considered yet
rm: not considered yet
rmdir: not considered yet
runcon: not considered yet
seq: not considered yet
shred: not considered yet
sleep: not considered yet
sort: at least --sort=month --sort=numeric is broken
split: not considered yet
stat: not considered yet
stdbuf: not considered yet
stty: not considered yet
sum: not considered yet
sync: not considered yet
tac: not considered yet
tail: not considered yet
tee: not considered yet
test: not considered yet
timeout: not considered yet
touch: not considered yet
truncate: not considered yet
tsort: not considered yet
tty: not considered yet
uname: not considered yet
unexpand: not considered yet
uniq: not considered yet
unlink: not considered yet
uptime: not considered yet
users: not considered yet
vdir: not considered yet
wc: not considered yet
who: not considered yet

Not a problem (solved / not affected / works already)

arch: no repeatable options
base32: fully handled, see #6007
base64: fully handled, see #6007
basename: fully handled, see #6018
basenc: fully handled, see #6007
cat: at least -u is broken, see #6034
chcon: at least -v is broken, see #6039
cksum: at least --base64 is broken, see #6041
cut: works already
dd: Seems to already work, not gonna touch it.
df: works already
dir: just defers to ls
dircolors: at least -p is broken, see #6150
dirname: at least -z is broken, see #6151
env: at least -i is broken, fixed by #6288
expand: works already
expr: works completely differently
factor: already works
false: has no flags/args
groups: has no flags/args
hashsum: not a GNU tool
head: works already
hostid: has no flags/args
hostname: works, BUT INCOMPLETE AND FRAGILE
link: has no flags/args
shuf: fully handled, see #5978 and #5989
tr: fully handled, see #6006
true: has no flags/args
whoami: no repeatable options
yes: no repeatable options

Begin with the unchecked utility entries in the issue and compare their repeated-flag behavior with GNU, starting with the explicitly broken flags. Treat each utility as complete when repeated flags no longer conflict where GNU accepts them, then update the checklist with the relevant result or linked work.

Written by the indexing model from the issue text.

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