[llvm] [lto pipeline] Add flag to skip module optimization passes in the prelink lto pipeline (PR #90364)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

I've tried making this change (without the flag) before in https://reviews.llvm.org/D148010, but never got around to chasing down all the rabbit holes. Adding this behind a flag should be fine.

It would be nice to have some test coverage for this (as in, for the optimization effect, not a pipeline test). Not entirely sure how to do that, I guess one would have a PhaseOrdering test that runs the pre-lto pipeline, then llvm-lto2(?) and then the post-lto pipeline?

https://github.com/llvm/llvm-project/pull/90364