[9.18] chg: dev: Use _exit() in the fatal() function

Since the fatal() isn't a correct but rather abrupt termination of the program, we want to skip the various atexit() calls because not all memory might be freed during fatal() call, etc. Using _exit() instead of exit() has this effect - the program will end, but no destructors or atexit routines will be called.

Backport of MR !8703 (merged)