PR remote/19496, internal err forking-threads-plus-bkpt

PR remote/19496, internal err forking-threads-plus-bkpt

This patch fixes an internal error that occurs in
gdb.threads/forking-threads-plus-breakpoint.exp:

/blah/binutils-gdb/gdb/target.c:2723: internal-error: Can't determine the
current address space of thread Thread 3170.3170

In default_thread_address_space, find_inferior_ptid couldn't find 3170.3170
because it had been overwritten in inferior_appeared, called as follows:

inferior_appeared
  remote_add_inferior
    remote_notice_new_inferior
      remote_update_thread_list

The cause of the problem was the following sequence of events:

* GDB knows only about the main thread

* the first fork event is reported to GDB, saved as pending_event

* qXfer:threads:read gets the threads from the remote.
  remove_new_fork_children id's the fork child from the pending event
  and removes it from the list reported to GDB.  All the rest of the
  threads, including the fork parent, are added to the GDB thread list.

* GDB stops all the threads.  All the stop events are pushed onto the
  stop reply queue behind the pending fork event.  The fork waitstatus
  is saved in the fork parent thread's pending status field
  thread_info.suspend.

* remote_wait_ns calls queued_stop_reply and process_stop_reply to
  remove the fork event from the front of the stop reply queue and save
  event information in the thread_info structure for the fork parent
  thread.  Unfortunately, none of the information saved in this way is
  the fork-specific information.

* A subsequent qXfer:threads:read packet gets the thread list including
  the fork parent and fork child.  remove_new_fork_children checks the
  thread list to see if there is a fork parent, doesn't find one, checks
  the stop reply queue for a pending fork event, doesn't find one, and
  allows the fork child thread to be reported to GDB before the fork
  event has been handled.  remote_update_thread_list calls
  remote_notice_new_thread and overwrites the current (main) thread in
  inferior_appeared.

So the fork event has been reported out of target_wait but it was left
pending on the infrun side (infrun.c:save_waitstatus).  IOW, the fork
event hasn't been processed by handle_inferior_event yet, so it hasn't
made it to tp->pending_follow yet.

The fix is to check thread_info.suspend along with the
thread_info.pending_follow in remote.c:remove_new_fork_children, to
prevent premature reporting of the fork child thread creation.

gdb/ChangeLog:

	PR remote/19496
	* remote.c (remove_new_fork_children): Check for pending
	fork status in thread_info.suspend.

gdb/testsuite/ChangeLog:

	PR remote/19496
	* gdb.threads/forking-threads-plus-breakpoint.exp (do_test):
	Remove kfail for PR remote/19496.