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

[Joel E. Denny via llvm-commits]

jdenny-ornl wrote:

> LLVM Buildbot has detected a new failure on builder `lldb-aarch64-ubuntu` running on `linaro-lldb-aarch64-ubuntu` while building `llvm` at step 6 "test".

This one blamed only me, but it looks irrelevant, and it passed on the next build.

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