Consistently use bool for fake_pid_p

Consistently use bool for fake_pid_p

I noticed a few spots where fake_pid_p is handled as an int, whereas
the field in struct inferior has type bool.  This patch changes the
remaining places to use bool as well.

Tested by the buildbot.

gdb/ChangeLog
2019-04-09  Tom Tromey  <tromey@adacore.com>

	* remote.c (remote_target::remote_add_inferior): Change fake_pid_p
	to bool.
	(extended_remote_target::attach): Update.
	(remote_target::remote_notice_new_inferior): Update.
	(remote_target::add_current_inferior_and_thread): Update.
	* inferior.c (exit_inferior_1): Use "false".
	* corelow.c (add_to_thread_list): Make fake_pid_p bool.