[clang] [llvm] [Offload] Change unregister library to use `atexit` instead of destructor (PR #86830)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

Fixed, I neglected the fact that OpenMP registers more destructors inside of the constructor itself. Passes all the tests now.

https://github.com/llvm/llvm-project/pull/86830