[clang] [llvm] [OffloadBundler] Rework the ctor of `OffloadTargetInfo` to support AMDGPU's generic target (PR #122629)

[Shilei Tian via llvm-commits]

shiltian wrote:

> Could we assume "gfx * -generic" is a single Target ID, and check for/parse that separately before doing rsplit on "-"?

I was thinking about it the other day but eventually gave up on it, because I want to keep this part as generic as possible instead of adding AMD special sauce here. I prefer not to do something like pattern matching stuff about `gfx`.

https://github.com/llvm/llvm-project/pull/122629