[lld] [RFC][lld][SPIRV] Add support for SPIR-V LTO (PR #178749)

[Nick Sarnie via llvm-commits]

sarnex wrote:

> The closest tool in tree is probably llvm-lto2 instead of lld, which lives in llvm/tools/
Yeah, calling out to `spirv-link` is only intended to be temporary to reduce the up-front cost, but who knows if someone will actually remove the dependence on it. Let me see if I can hook up `clang` to call `llvm-lto2`.


https://github.com/llvm/llvm-project/pull/178749