* target.h (struct target_ops): Add new field to_get_ada_task_ptid.

    * target.h (struct target_ops): Add new field to_get_ada_task_ptid.
        (target_get_ada_task_ptid): New macro.
        * target.c (default_get_ada_task_ptid): New function.
        (update_current_target): Inherit field default_get_ada_task_ptid.
        (update_current_target): Make default_get_ada_task_ptid the default
        value for field to_get_ada_task_ptid.
        * ada-lang.h (struct task_control_block): Delete. Never used.
        (struct task_ptid, task_ptid_t, struct task_entry, task_list):
        Likewise.
        (struct ada_task_info): New.
        (ada_task_is_alive, ada_find_printable_frame)
        (ada_task_list_iterator_ftype, iterate_over_live_ada_tasks): Add
        declarations.
        (ada_build_task_list): Update prototype.
        (init_task_list, ada_is_exception_breakpoint): Remove prototypes.
        * ada-lang.c (ada_find_printable_frame): Make non-static.
        * ada-tasks.c: New file.
        * Makefile.in (SFILES): Add ada-tasks.c.
        (COMMON_OBS): Add ada-tasks.o.
        * linux-thread-db.c (thread_db_find_thread_from_tid)
        (thread_db_get_ada_task_ptid): New functions.
        (init_thread_db_ops): Set thread_db_ops.to_get_ada_task_ptid.