include oneMKL interface when building the SYCL compiler

[zjin-lcf]

It may be desirable that when users build the SYCL compiler from source with CUDA/HIP support, they can add some flag to the Python script to build the oneMKL interface (https://github.com/oneapi-src/oneMKL)

1 a user clones two repositories
2 a user puts the oneMKL repo somewhere in the llvm repo
3. a user can add a flag to the Python script to optionally build the oneMKL interface