[data_loader] Extra signal handlers in DataLoader.cpp should be added on top rather than replacing defaults (#103164)
Summary: DataLoader.cpp signal handlers are adding some special behavior (e.g. exit(0) on SIGTERM under certain conditions). To preserve this behavior we should install additional signal handlers on top of default ones, rather than completely replacing them.
Test Plan: unit tests
Reviewed By: drej82
Differential Revision: D46525348
Pull Request resolved: https://github.com/pytorch/pytorch/pull/103164
Approved by: https://github.com/drej82
