tracing: Export trace_dump_stack to modules

There is no reason for this function to be unexprted and it's a useful
debugging aid.

Link: http://lkml.kernel.org/r/1539759103-5923-1-git-send-email-nborisov@suse.com

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -2727,6 +2727,7 @@ void trace_dump_stack(int skip)
 	__ftrace_trace_stack(global_trace.trace_buffer.buffer,
 			     flags, skip, preempt_count(), NULL);
 }
+EXPORT_SYMBOL_GPL(trace_dump_stack);
 
 static DEFINE_PER_CPU(int, user_stack_count);