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

[Fangrui Song via llvm-commits]

https://github.com/MaskRay requested changes to this pull request.

I have a fundamental concern with this approach. This is not really a linker - it's a bitcode -> SPIR-V tool that shells out to an external tool (spirv-link) for the actual linking. Adding a new lld flavor has significant maintenance cost: every change to lld/Common, Driver.h, LLD_ALL_DRIVERS. The closest tool in tree is probably llvm-lto2 instead of lld, which lives in llvm/tools/

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