QFileSystemWatcher/Linux: don't print warnings for benign cases

ENOENT (no such file or directory) is a benign error, since it could
happen also out of a race condition. All the other errors in the
inotify_add_watch(2) man page indicate bugs in Qt or resource
exhaustion, so those remain being printed.

Task-number: QTBUG-68586
Change-Id: I04b94079b6da48f39a82fffd1535c08d8a3d8c33
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: David Faure <david.faure@kdab.com>

src/corelib/io/qfilesystemwatcher_inotify.cpp

@@ -302,7 +302,8 @@ QStringList QInotifyFileSystemWatcherEngine::addPaths(const QStringList &paths,
                                        | IN_DELETE_SELF
                                        )));
         if (wd < 0) {
-            qWarning().nospace() << "inotify_add_watch(" << path << ") failed: " << QSystemError(errno, QSystemError::NativeError).toString();
+            if (errno != ENOENT)
+                qErrnoWarning("inotify_add_watch(%ls) failed:", path.constData());
             continue;
         }