gdb/infrun: enable/disable thread events of all targets in stop_all_threads

In stop_all_threads, the thread events of the current top target are
enabled at the beginning of the function and then disabled at the end
(at scope exit time).  Because there may be multiple targets whose
thread lists will be updated and whose threads are stopped,
enable/disable thread events for all targets.

This update caused a change in the annotations.  In particular, a
"frames-invalid" annotation is printed one more time due to switching
the current inferior.  Hence, gdb.base/annota1.exp and
gdb.cp/annota2.exp tests are also updated.

Regression-tested on X86_64 Linux using the default board file and the
native-extended-gdbserver board file.

gdb/ChangeLog:
2020-05-14  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>

	* infrun.c (stop_all_threads): Enable/disable thread events of all
	targets.  Move a debug message denoting the end of the function
	into the SCOPED_EXIT block.

gdb/testsuite/ChangeLog:
2020-05-14  Tankut Baris Aktemur  <tankut.baris.aktemur@intel.com>

	* gdb.base/annota1.exp: Update the expected output.
	* gdb.cp/annota2.exp: Ditto.

1 files changed, 19 insertions, 5 deletions

diff --git a/gdb/infrun.c b/gdb/infrun.c
index c5bf2d0..2a8e73c 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -4769,8 +4769,25 @@ stop_all_threads (void)
 
   scoped_restore_current_thread restore_thread;
 
-  target_thread_events (1);
-  SCOPE_EXIT { target_thread_events (0); };
+  /* Enable thread events of all targets.  */
+  for (auto *target : all_non_exited_process_targets ())
+    {
+      switch_to_target_no_thread (target);
+      target_thread_events (true);
+    }
+
+  SCOPE_EXIT
+    {
+      /* Disable thread events of all targets.  */
+      for (auto *target : all_non_exited_process_targets ())
+	{
+	  switch_to_target_no_thread (target);
+	  target_thread_events (false);
+	}
+
+      if (debug_infrun)
+	fprintf_unfiltered (gdb_stdlog, "infrun: stop_all_threads done\n");
+    };
 
   /* Request threads to stop, and then wait for the stops.  Because
      threads we already know about can spawn more threads while we're
@@ -4961,9 +4978,6 @@ stop_all_threads (void)
 	    }
 	}
     }
-
-  if (debug_infrun)
-    fprintf_unfiltered (gdb_stdlog, "infrun: stop_all_threads done\n");
 }
 
 /* Handle a TARGET_WAITKIND_NO_RESUMED event.  */