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/mmapmodule.c

@@ -1221,7 +1221,6 @@ new_mmap_object(PyTypeObject *type, PyObject *args, PyObject *kwdict)
         fd = devzero = _Py_open("/dev/zero", O_RDWR);
         if (devzero == -1) {
             Py_DECREF(m_obj);
-            PyErr_SetFromErrno(PyExc_OSError);
             return NULL;
         }
 #endif