change BuildExtension.with_options to return a class not a c-tor (pytorch#40121)

Summary: Pull Request resolved: pytorch#40121

Test Plan: Imported from OSS

Reviewed By: ezyang

Differential Revision: D22076634

Pulled By: pbelevich

fbshipit-source-id: a89740baf75208065e418d7f972eeb52db9ee3cf

Author: pbelevich

torch/utils/cpp_extension.py

@@ -312,14 +312,15 @@ class BuildExtension(build_ext, object):
     @classmethod
     def with_options(cls, **options):
         r'''
-        Returns an alternative constructor that extends any original keyword
+        Returns a subclass with alternative constructor that extends any original keyword
         arguments to the original constructor with the given options.
         '''
-        def init_with_options(*args, **kwargs):
-            kwargs = kwargs.copy()
-            kwargs.update(options)
-            return cls(*args, **kwargs)
-        return init_with_options
+        class cls_with_options(cls):
+            def __init__(self, *args, **kwargs):
+                kwargs.update(options)
+                super().__init__(*args, **kwargs)
+
+        return cls_with_options
 
     def __init__(self, *args, **kwargs):
         super(BuildExtension, self).__init__(*args, **kwargs)