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

[Jacob Lambert via llvm-commits]

lamb-j wrote:

Could we possibly do a phase-out approach?

For COV5 and earlier we keep the current strategy, allowing both 3 and 4 field triples

For COV6 (including generics), we enforce the 4 field triples

This could help us not break things internally, and then as tools and APIs update to V6, they can also update to 4-field triples

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