* linux-thread-db.c: Include "linux-nat.h".

	* linux-thread-db.c: Include "linux-nat.h".
	(check_for_thread_db): New function, split out from
	thread_db_new_objfile.  Remove dead check for active
	thread_db on inapplicable targets.
	(thread_db_new_objfile): Call check_for_thread_db.
	* Makefile.in (linux-thread-db.o): Update.
	* linux-nat.c (child_post_attach): Call check_for_thread_db.
	(linux_child_post_startup_inferior): Likewise.
	(lin_lwp_attach_lwp): Call target_post_attach instead of
	child_post_attach.
	* linux-nat.h (check_for_thread_db): New prototype.