Sometimes stacks for at_exit callbacks don't include any of the user functions/files.
For example, a race with a global std container destructor will only contain
the container type name and our at_exit_wrapper function. No signs what global variable
this is.
Remember and include in reports the function that installed the at_exit callback.
This should give glues as to what variable is being destroyed.
Depends on D114606.
Reviewed By: vitalybuka, melver
Differential Revision: https://reviews.llvm.org/D114607
Add a test for a common C++ bug when a global object is destroyed
while background threads still use it.
Depends on D114604.
Reviewed By: vitalybuka, melver
Differential Revision: https://reviews.llvm.org/D114605
