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

[Nick Sarnie via cfe-commits]

sarnex wrote:

In our specific case we don't need to run optimizations on the `llvm-link` output immediately as it will be optimized when it's used in a larger compilation command, but I can see the use case in general.

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