pythongh-127945: make initialization of error_object_name thread safe in ctypes (python#131896)

Author: kumaraditya303

Modules/_ctypes/_ctypes.c

@@ -6093,14 +6093,19 @@ _ctypes_mod_exec(PyObject *mod)
     }
 
 #ifdef WORDS_BIGENDIAN
-        st->swapped_suffix = PyUnicode_InternFromString("_le");
+    st->swapped_suffix = PyUnicode_InternFromString("_le");
 #else
-        st->swapped_suffix = PyUnicode_InternFromString("_be");
+    st->swapped_suffix = PyUnicode_InternFromString("_be");
 #endif
     if (st->swapped_suffix == NULL) {
         return -1;
     }
 
+    st->error_object_name = PyUnicode_InternFromString("ctypes.error_object");
+    if (st->error_object_name == NULL) {
+        return -1;
+    }
+
     if (_ctypes_add_types(mod) < 0) {
         return -1;
     }

Modules/_ctypes/callproc.c

@@ -164,12 +164,7 @@ _ctypes_get_errobj(ctypes_state *st, int **pspace)
                         "cannot get thread state");
         return NULL;
     }
-    if (st->error_object_name == NULL) {
-        st->error_object_name = PyUnicode_InternFromString("ctypes.error_object");
-        if (st->error_object_name == NULL) {
-            return NULL;
-        }
-    }
+    assert(st->error_object_name != NULL);
     if (PyDict_GetItemRef(dict, st->error_object_name, &errobj) < 0) {
         return NULL;
     }