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

[Yaxun Liu via cfe-commits]

yxsamliu wrote:

LGTM. I think it is useful to let clang have a light-weight interface to llvm-link for IR linking where lld does not quite fit. Structurally, this PR does not make existing code worse.

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