MDEV-29951 server hang in crash handler

When trying to output stacktrace, and addr2line is not installed, the
child process forked by start_addr2line_fork() will fail to do exec(),
and finish with exit(1).

There is a problem with exit() though - it runs exit handlers,
and for the forked copy of crashing process, it is a bad idea.

In 10.5+ code for example, exit handlers include
tpool::task_group static destructors, and it will hang infinitely
waiting for completion of the outstanding tasks.

The fix is to use _exit() instead, which skips the execution of exit
handlers

mysys/my_addr_resolve.c

@@ -202,7 +202,7 @@ int start_addr2line_fork(const char *binary_path)
     close(out[0]);
     close(out[1]);
     execlp("addr2line", "addr2line", "-C", "-f", "-e", binary_path, NULL);
-    exit(1);
+    _exit(1);
   }
 
   close(in[0]);