[clang] [llvm] [fatlto] Use the ThinLTO default pipeline for FatLTO (PR #134434)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

Switching to the ThinLTO post-link pipeline will have a big impact on optimization behavior and compile-time. I think it would be safer to make a change along the lines of https://github.com/llvm/llvm-project/pull/126168, i.e. to schedule the necessary passes in the FatLTO pipeline. Without having looked into it closely, it would probably be okay to just schedule them before the buildModuleOptimizationPipeline call.

https://github.com/llvm/llvm-project/pull/134434