test.pl: Try alarm if can't start watchdog on Win/VMS

Prior to this commit, the code gave up immediately if it tried
unsuccessfully to use a watchdog thread.  But the alarm method is still
available.  Drop down to try it.

Author: khwilliamson

t/test.pl

@@ -1947,18 +1947,19 @@ ($;$)
                     $watchdog = system(1, $cmd);
                 }
             };
-            if ($@ || ($watchdog <= 0)) {
-                _diag('Failed to start watchdog');
-                _diag($@) if $@;
-                undef($watchdog);
-                return;
-            }
+
+            if (! $@ && $watchdog > 0) {
 
             # Add END block to parent to terminate and clean up watchdog
             # process
             eval("END { local \$! = 0; local \$? = 0;
                         wait() if kill('KILL', $watchdog); };");
             return;
+            }
+
+            $@ = "\n$@" if $@;
+            _diag("Failed to start watchdog$@\nTrying alternate method");
+            goto WATCHDOG_VIA_ALARM;
         }
 
         # Try using fork() to generate a watchdog process