[libcxx-commits] [libcxxabi] [libc++abi] Revert gating of `__cxa_thread_atexit` on Linux||Fuchsia (PR #186054)

[Louis Dionne via libcxx-commits]

ldionne wrote:

@whitequark Could you confirm whether the PR in its current form fixes the original issue you were seeing? It would be sad if my refactoring ended up not solving the original problem :)

https://github.com/llvm/llvm-project/pull/186054