gdb/

gdb/
	* linux-thread-db.c (inferior_has_bug): New function.
	(thread_db_find_new_threads_silently): Return boolean as checked by
	inferior_has_bug, describe it in the comments.
	(try_thread_db_load_1): Move call to thread_db_find_new_threads_silently
	earlier.  Abort the initialization if it returned non-zero.
	(thread_db_find_new_threads_2): Preinitialize ERR.  Check errors also
	if UNTIL_NO_NEW,

gdb/testsuite/
	* gdb.threads/gcore-thread.exp: Remove variable libthread_db_seen.
	Wrap the test into loop for corefile and core0file.