Move CUDAGuard, CUDAStream and CUDAGuardImpl to c10/cuda (#14248)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/14248
This diff also introduces a horrifying hack to override CUDA's DeviceGuardImpl
with a HIPGuardImplMasqueradingAsCUDA, to accommodate PyTorch's current
behavior of pretending CUDA is HIP when you build with ROCm enabled.
Reviewed By: bddppq
Differential Revision: D13145293
fbshipit-source-id: ee0e207b6fd132f0d435512957424a002d588f02
