Split CUDA_NVCC_FLAGS by space (#44603)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/44599
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44603
Reviewed By: albanD
Differential Revision: D23692320
Pulled By: ezyang
fbshipit-source-id: 6a63d94ab8b88e7a82f9d65f03523d6ef639c754
