[flang] [llvm] [flang-rt] Add experimental support for GPU build (PR #131826)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> LGTM.
> 
> The `gpu_sources` list will probably evolve over time, fixing more and more. It might actually a good idea to have a separate list until it stabilized.

What I figured, could you look at https://github.com/llvm/llvm-project/pull/131695 as well? I think in the future we'll need to think of how to run tests for this and investigating setting up the missing files.

https://github.com/llvm/llvm-project/pull/131826