[clang] [Offload] Treat an empty packager archicture as 'generic' (PR #126655)

[Michael Kruse via cfe-commits]

Meinersbur wrote:

What happens with `-march` not specified? I only know about gcc falling back on `-march=x86-64`, but depends on the target triple.

https://github.com/llvm/llvm-project/pull/126655