Report error when ATEN_THEADING is OMP and USE_OPENMP is turned off. (#40146)
Summary:
Currently, even if USE_OPENMP is turned off, ATEN_THEADING can still use OpenMP. This commit fixes it.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40146
Reviewed By: ezyang
Differential Revision: D22208758
Pulled By: pbelevich
fbshipit-source-id: 0866c9bb9b3b5b99d586aed176eb0fbe177efa4a
