cp: link-deref gnu test fix

[matrixhead]

this pr tries to fix gnu test case "link deref" for cp utility
these are the changes made:

1. when trying to copy a folder without -R before throwing "-r not specified" error, cp would make sure that source is not a symlink and noderef option is not given. This way, when both of them are given, it would treat it as a file and copy the symlink itself.

2. to match gnu cp's behavior, -R won't disable dereference if --link is given

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/cp/link-deref is no longer failing!
Skipping an intermittent issue tests/tail/inotify-dir-recreate (passes in this run but fails in the 'main' branch)

[BenWiederhake]

LGTM, except that one typo. (I understand that the typo is also present in the already-existing code; feel free to keep it or fix it as you see fit.)

(Remaining CI failures are known issues #6275 and #6333, so out of scope for this PR.)

Before I merge this, I want to give the other maintainers an opportunity to look at it, because I don't feel 100% confident around symlinks. But this seems very reasonable.

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/cp/link-deref is no longer failing!

[BenWiederhake]

LGTM. I'll wait for a few days for the others too look at it, because I don't feel 100% confident around the symlink code.

[matrixhead]

is it because I tried to squeeze in deref logic into parsing code

[sylvestre]

well done!