[llvm] [Offload] Stop using global ctor/dtors in Offload unit tests (PR #149299)

[Callum Fare via llvm-commits]

callumfare wrote:

I didn't fully understand why the fix in #148642 worked, because the plugins were showing up as uninitialized before `deinit()` was ever called on them. My assumption is that's because plugin objects were being clobbered during teardown, but I don't actually know if that's the case. This seemed like a sensible change either way.

https://github.com/llvm/llvm-project/pull/149299