[clang] [flang] [Flang-new][OpenMP] Add offload related flags for AMDGPU (PR #96742)

[Joseph Huber via cfe-commits]

https://github.com/jhuber6 approved this pull request.

The fact that it's called `-fcuda-is-device` is historical cruft, but I guess it's easiest to just work with it. I also hate `-mlink-builtin-bitcode` as a concept, but we're not quite ready to move away from its hacks unfortunately. 

https://github.com/llvm/llvm-project/pull/96742