Include missing header (#97453)
`std::exception_ptr` is defined in `<exception>`. This works in the past because the header is transitively included by other headers. The situation has changed in most recent llvm (https://github.com/llvm/llvm-project/commit/c9d36bd80760db14f14b33789e6cbc6cb8c64830)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97453
Approved by: https://github.com/ngimel
