[clang] [llvm] [HIPSPV] Add in-tree SPIR-V backend support for chipStar (PR #206910)

[Henry Linjamäki via cfe-commits]

linehill wrote:

> > But it’s fine in case the backend is not yet good enough for chipStar
> 
> the native backend is preferred. The idea being that if you are planning on using the SPIR-V Translator, you build LLVM with it and then prefer using it. Otherwise we default to using the native backend.

That could be workable for me if `llvm-spirv` in the PATH are considered last. Something like:

1) if `llvm-spirv` is built along side with LLVM (= it is in clang's driver path), the translator would be used, otherwise
2) use the backend if it is built and otherwise
3) pick `llvm-spirv` from PATH.

But maybe it's simpler and more reliable just to have a configuration flag to choose between the backend and the translator than implement the above logic.

The current logic in the patch would prevent me using the SPIR-V backend because I have `llvm-spirv` in PATH needed for other projects.


https://github.com/llvm/llvm-project/pull/206910