[llvm] [OFFLOAD] Add support for host offloading device (PR #177307)

[Joseph Huber via llvm-commits]

https://github.com/jhuber6 commented:

I would like this to be simplified in general. There's a lot of checks that this could remove that are like `device->device` (because the host device was just null). At a minimum this should include a test that uses the host device, 

https://github.com/llvm/llvm-project/pull/177307