Kernel: Dump backtrace on exit() syscall.

This makes assertion failures a lot more pleasant to investigate.

Kernel/Process.cpp

@@ -644,6 +644,8 @@ void Process::sys$exit(int status)
     kprintf("sys$exit: %s(%u) exit with status %d\n", name().characters(), pid(), status);
 #endif
 
+    dump_backtrace(ksyms_ready);
+
     m_termination_status = status;
     m_termination_signal = 0;
     die();