[llvm] [LTO] Avoid assert fail on failed pass plugin load (PR #96691)

[via llvm-commits]

https://github.com/serge-sans-paille commented:

I'm not 100% sure we shouldn't stop the whole pipeline when the module fails to load. The difference in behavior between opt and llvm-lto2 is probably not a good thing :-/

https://github.com/llvm/llvm-project/pull/96691