Use global variables to register the return_types namedtuples (#108832)

Fixes #69221. Builds on top of #107000, fixing the buck build issue linked [here](https://github.com/pytorch/pytorch/pull/107000#issuecomment-1708857375).

Pull Request resolved: https://github.com/pytorch/pytorch/pull/108832
Approved by: https://github.com/zou3519
diff --git a/tools/BUCK.bzl b/tools/BUCK.bzl
index 25c85af..7ad0882 100644
--- a/tools/BUCK.bzl
+++ b/tools/BUCK.bzl
@@ -132,6 +132,7 @@
             "autograd/templates/python_linalg_functions.cpp",
             "autograd/templates/python_nested_functions.cpp",
             "autograd/templates/python_nn_functions.cpp",
+            "autograd/templates/python_return_types.h",
             "autograd/templates/python_return_types.cpp",
             "autograd/templates/python_sparse_functions.cpp",
             "autograd/templates/python_special_functions.cpp",