[clang] [HIP] change default offload archs (PR #139281)

[Yaxun Liu via cfe-commits]

yxsamliu wrote:

> I think that in general we also need to decide on what happens when you pick an amdgcn— triple. IMHO for that case we should probably error out if no mcpu is provided, since there’s no reasonable default, except for “all”, but that would be incredibly disruptive.

That happens for device libs. In that case the default processor is "generic", and clang emits LLVM IR not assuming any target processor. I think for emitting LLVM IR we should allow that. We can emit error if it emits assembly or objects.

https://github.com/llvm/llvm-project/pull/139281