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

[Nick Sarnie via cfe-commits]

sarnex wrote:

> LLD can link LLVM, do LTO and emit SPIR-V with SPIR-V backend (or LLVM bitcode with -emit-llvm option). Have you considered using LLD for OpenMP device RTL?

But it can't actually link SPIR-V, so we can't use it when we aren't using LTO, so we would only ever `lld` when LTO is enabled, which seems somewhat weird.

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