[CUDA][HIP] Support '--offload-arch=native' for the new driver

This patch applies the same handling for the `--offload-arch=native'
string to the new driver. The support for OpenMP will require some extra
logic to infer the triples from the derived architecture strings.

Depends on D141051

Reviewed By: tra

Differential Revision: https://reviews.llvm.org/D141078