[goalc] improve reliability of debugger tests (#898)

* try fixing debugger test

* poke first

* debug print

* another try on debug prints

* start watcher after we did a break

* cleanup print statements, use sleep_for instead of usleep

goalc/debugger/Debugger.cpp

@@ -95,10 +95,10 @@ bool Debugger::attach_and_break() {
   if (is_valid() && !m_attached) {
     // reset and start the stop watcher
     clear_signal_queue();
-    start_watcher();
 
     // attach and send a break command
     if (xdbg::attach_and_break(m_debug_context.tid)) {
+      start_watcher();
       // wait for the signal queue to get a stop and pop it.
       auto info = pop_signal();