infrun.c: add for_each_just_stopped_thread

infrun.c: add for_each_just_stopped_thread

This is a preparatory/cleanup patch that does two things:

- Renames 'delete_step_thread_step_resume_breakpoint'.  The
  "step_resume" part is misnomer these days, as the function deletes
  other kinds of breakpoints, not just the step-resume breakpoint.  A
  following patch will want to make it delete yet another kind of
  breakpoint, even.

- Splits out the logic of which threads get those breakpoints deleted
  to a separate "for_each"-style function, so that the same following
  patch may use it with a different callback.

Tested on x86_64 Fedora 20.

gdb/
2014-10-15  Pedro Alves  <palves@redhat.com>

	* infrun.c (delete_step_resume_breakpoint_callback): Delete.
	(delete_thread_infrun_breakpoints): New function, with parts
	salvaged from delete_step_resume_breakpoint_callback.
	(delete_step_thread_step_resume_breakpoint): Delete.
	(for_each_just_stopped_thread_callback_func): New typedef.
	(for_each_just_stopped_thread): New function.
	(delete_just_stopped_threads_infrun_breakpoints): New function.
	(delete_step_thread_step_resume_breakpoint_cleanup): Rename to ...
	(delete_just_stopped_threads_infrun_breakpoints_cleanup):
	... this.  Adjust.
	(wait_for_inferior, fetch_inferior_event): Adjust to renames.