Only do TLS access when necessary in basicAutogradNotImplementedFallback (#105845)
This is an optimization that may or may not matter (it's difficult to
see the impact on benchmarks).
This PR is a resubmit of #105737 to go directly through github first.
Test Plan:
- existing tests
Pull Request resolved: https://github.com/pytorch/pytorch/pull/105845
Approved by: https://github.com/soulitzer
