[clang] [clang][Driver][SPIR-V] Allow linking IR using llvm-link (PR #169572)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

I do see the value in being able to do this from the compiler do we don't need as many hacks. Another consideration is that we'd want to optimize the IR further after it's linked, which `llvm-link` itself doesn't do as far as I know. Would it be possible to do this via `-fuse-ld=llvm-link` or something similar?

https://github.com/llvm/llvm-project/pull/169572