[issue35923] Update the BuiltinImporter in importlib to use loader._ORIGIN instead of a hardcoded value

[Ned Deily]

Change by Ned Deily <nad at python.org>:


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nosy: +brett.cannon, eric.snow, ncoghlan

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35923>
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