install: implement option -C

[sylvestre]

No description provided.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/install/install-C is no longer failing!

[cakebaker]

I don't know if you have seen it: test_install_compare_special_mode_bits fails on FreeBSD:

thread 'test_install::test_install_compare_special_mode_bits' panicked at tests/by-util/test_install.rs:1716:10:
      Command was expected to succeed. code: 1
      stdout = removed 'dest_file'
  
       stderr = install: dest_file: chmod failed with error Inappropriate file type or format (os error 79)
      install: failed to chmod 'dest_file'

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/install/install-C is no longer failing!

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/install/install-C is no longer failing!

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/misc/stdbuf (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/install/install-C is no longer failing!

[cakebaker]

I noticed that GNU install shows some warning on stderr when using special mode bits:

$ install -Cv -m1755 source dest 
install: the --compare (-C) option is ignored when you specify a mode with non-permission bits
removed 'dest'
'source' -> 'dest'

We don't show such a warning. Is that on purpose?

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/tee (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/install/install-C is no longer failing!

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/tee (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/timeout/timeout (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/install/install-C is no longer failing!

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/install/install-C is no longer failing!

[cakebaker]

Congrats! The gnu test tests/install/install-C is no longer failing!

Great, good work :)