Synchronizing LTO code-generation configuration between Clang and LLD (DTLTO)

[Pierre-vh]

@kbelochapka

We will most likely follow Steven Wu’s suggestion: serialize llvm::TargetOptions and lto::Config into bitcode, with round-trip checks in assert builds to catch drift

Do you have a timeline for this ? I could make use of this in https://discourse.llvm.org/t/rfc-use-a-cache-for-parallel-fulllto-codegen/