* linux-thread-db.c (thread_db_new_objfile): Only try to load

	* linux-thread-db.c (thread_db_new_objfile): Only try to load
	libthread_db when we load libpthread or the main symbol file.
	(thread_db_inferior_created): New function.
	(_initialize_thread_db): Attach inferior_created observer.
	* linux-nat.c (linux_child_post_attach): Remove call to
	check_for_thread_db.
	(linux_child_post_startup_inferior): Ditto.
	* objfiles.h (OBJF_MAINLINE): Define.
	* symfile.c (symbol_file_add_with_addrs_or_offsets): Pass it to
	allocate_objfile when appropriate.