cat: handle broken pipe gracefully

[tgrez]

Fixes #6876.

I was able to reproduce the original issue with both:

$ echo a | gzip -c > f.gz
$ perl -e '
      use POSIX qw(dup2);
      $SIG{PIPE} = "DEFAULT";
      pipe my ($read_end, $write_end);
      dup2 fileno $write_end, 1;
      close $read_end;
      exec "cat", "f.gz", "f.gz";
  '

cat: f.gz: EPIPE: Broken pipe
cat: f.gz: EPIPE: Broken pipe

and:

$ cat f.gz | false
cat: f.gz: EPIPE: Broken pipe

This PR fixes both cases.

Preparing yet another similar fix (previous ones: #8327 and #8312) I wonder if it makes sense to fix it for all binaries in a single place (at least for non-windows platforms), like in uucore::main macro in src/uucore_procs/src/lib.rs:

             // disable rust signal handlers (otherwise processes don't dump core after e.g. one SIGSEGV)
             #[cfg(unix)]
             uucore::disable_rust_signal_handlers().expect("Disabling rust signal handlers failed");
+            // When we receive a SIGPIPE signal, we want to terminate the process so
+            // that we don't print any error messages to stderr. Rust ignores SIGPIPE
+            // (see https://github.com/rust-lang/rust/issues/62569), so we restore it's
+            // default action here.
+            #[cfg(not(target_os = "windows"))]
+            unsafe {
+                libc::signal(libc::SIGPIPE, libc::SIG_DFL);
+            }
             let result = uumain(args);
             match result {
                 Ok(()) => uucore::error::get_exit_code(),

I can update this PR if such general fix makes sense.

[tgrez]

Also, assuming those fish shell tests are located here: https://github.com/fish-shell/fish-shell/blob/e9bb150a41b64bc0d4cd3784d6fd54e0eabb4b42/tests/checks/pipestatus.fish#L200

This bug:

$ cat /dev/zero | dd > /not/a/valid/path
bash: /not/a/valid/path: No such file or directory
cat: /dev/zero: EPIPE: Broken pipe

is also fixed (verified in bash shell, but the error message is no longer present):

$ cat /dev/zero | dd > /not/a/valid/path
bash: /not/a/valid/path: No such file or directory
$

[tgrez]

Setting to draft until CI errors are resolved.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/misc/stdbuf (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/misc/tee (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)

[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/du/inodes is no longer failing!

[RenjiSann]

Thanks !