In non-stop mode, exec commands apply only to the current thread.
We can add a mechanism to resume all threads.  In a frontend
perpective, I'm not clear if we should implement
-exec-continue --all, -exec-continue --thread="all", or just
require the frontend to do the:

for each thread in stopped threads
  resume thread
done

In CLI,  "thread apply all continue&" works too, but it feels
to longuish to type?

Opinions?  Import mi-getopt into common code and use it in CLI?

-- 
Pedro Alves