Run pthreadpool with _NoPThreadPoolGuard on the same thread (#58759)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58759
* Makes `pthreadpool()->run` respect `_NoPThreadPoolGuard`
Runs tasks on the same thread instead of parallelizing when guard is present
Test Plan:
buck build //xplat/caffe2:aten_test_test_thread_pool_guard
./buck-out/last/aten_test_test_thread_pool_guard
Reviewed By: kimishpatel
Differential Revision: D28597425
fbshipit-source-id: 0365ad9947c239f5b37ce682802d4d401b8b0a48
