[llvm] [OFFLOAD] Add plugin with support for Intel oneAPI Level Zero (PR #158900)

[Piotr Balcer via llvm-commits]

pbalcer wrote:

> @adurang I'm now getting compile errors because apparently the L0 plugin is using `ompt_device_t` . Even if it did compile, I think the issue is still present.
> 
> `OL_PLATFORM_BACKEND_LEVEL_ZERO` needs adding to `ol_platform_backend_t` and handled in all the places that it is used.
> 
> However, thinking about it, I think it might make sense to add liboffload support in another MR and keep this one focusing on libopenmp.

I just tried it, by hacking around the compile errors, and I'm not seeing the platform. But I might have made some other mistakes - I didn't have the chance to debug what's happening yet.

https://github.com/llvm/llvm-project/pull/158900