- Pass `blas.provider` into `buildInputs`, so that CMake can find the actual
`mkl` for inspection of its cmake files and headers.
- Add `USE_MKL` correctly when the blas provider is `mkl`.
- Use the MKLDNN and MKLDNN_CBLAS flags by default, since `mkldnn` is FOSS and
always available..
- Remove a patch for MKL 2019, since we've moved to 2020.
- Add a pythonImportsCheck for "torch" as a basic sanity-check
- Removed some unused variables at the top of the file