tsan: remember and print function that installed at_exit callbacks

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