Issue #23694: Enhance _Py_open(), it now raises exceptions

* _Py_open() now raises exceptions on error. If open() fails, it raises an
  OSError with the filename.
* _Py_open() now releases the GIL while calling open()
* Add _Py_open_noraise() when _Py_open() cannot be used because the GIL is not
  held

Modules/_posixsubprocess.c

@@ -257,6 +257,7 @@ _close_open_fds_safe(int start_fd, PyObject* py_fds_to_keep)
     fd_dir_fd = _Py_open(FD_DIR, O_RDONLY);
     if (fd_dir_fd == -1) {
         /* No way to get a list of open fds. */
+        PyErr_Clear();
         _close_fds_by_brute_force(start_fd, py_fds_to_keep);
         return;
     } else {