clean up pending threads on fork

[TingDaoK]

Issue #, and/or reason for changes (REQUIRED):

• When the process gets forked, the threads are NOT get copied.
• But we have a lazy thread join method may copy the state of the threads that needs to be joined from the parent process.
• So, when the child process tries to clean up the global state of the threads to be cleaned, it picks the threads info copied from parent process, and it's meaningless to the child process, which leads to a segfault.
• https://man7.org/linux/man-pages/man2/fork.2.html

Description of changes:

• Try to register a handler to clean up the global state from the parent process before fork, so that child will not inherit the global state.
• https://man7.org/linux/man-pages/man3/pthread_atfork.3.html

TODO

• This is likely not gonna solve all issues for fork but at least, it will solve the segfault we see
• What will happen to windows?
• we need to dive much deep into the fork, and how to deal with it with multiple background threads, just throw out ideas:
  • don't allow it?
  • call exec()?
  • join all threads?

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 11.11111% with 8 lines in your changes missing coverage. Please review.

Project coverage is 84.11%. Comparing base (568f46b) to head (88ad60a).

Files with missing lines	Patch %	Lines
source/thread_shared.c	0.00%	7 Missing ⚠️
source/common.c	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1181      +/-   ##
==========================================
- Coverage   84.23%   84.11%   -0.12%     
==========================================
  Files          57       57              
  Lines        5980     5988       +8     
==========================================
  Hits         5037     5037              
- Misses        943      951       +8     

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