Add some casts for building on musl.

Add some casts for building on musl.

gdb/ChangeLog:

	* linux-thread-db.c (find_new_threads_callback): Cast ti.ti_tid to
	unsigned long for debug_printf.
	(thread_db_pid_to_str): Ditto.

gdb/gdbserver/ChangeLog:

	* thread-db.c (find_one_thread): Cast ti.ti_tid to unsigned long
	for debug_printf.
	(attach_thread, find_new_threads_callback): Ditto.