deadlock: print a more explicit message when pthread_mutex_unlock can…

…'t be attached

Most likely, this happen because of a missing --binary argument. Let's
be friendly to our user and print a more useful messsage.

tools/deadlock.py

@@ -483,7 +483,7 @@ def main():
  pid=args.pid,
  )
  except Exception as e:
- print('%s. Failed to attach to symbol: %s' % (str(e), symbol))
+ print('%s. Failed to attach to symbol: %s\nIs --binary argument missing?' % (str(e), symbol))
  sys.exit(1)
  for symbol in args.lock_symbols:
  try: