* Also defer signals while registering fork hooks.
* While malloc provides fork heap hooks which lock the heaps and unlock/reinit,
malloc_debug provides empty hooks.
* Ideas suggested by Ingo, patch reviewed by him. Thanks a lot!
* Also call fork parent hooks on failure.
* Solve locks-up when combining multithreading and process forking, should help
with #13111.
17b2a3cfcb