gdb: bool-ify follow_fork

gdb: bool-ify follow_fork

Change parameters and return value of the various follow_fork
functions/methods from int to bool.

gdb/ChangeLog:

	* fbsd-nat.c (fbsd_nat_target::follow_fork): Change bool to int.
	* fbsd-nat.h (class fbsd_nat_target) <follow_fork>: Likewise.
	* inf-ptrace.c (inf_ptrace_target::follow_fork): Likewise.
	* inf-ptrace.h (struct inf_ptrace_target) <follow_fork>: Likewise.
	* infrun.c (follow_fork): Likewise.
	(follow_fork_inferior): Likewise.
	* linux-nat.c (linux_nat_target::follow_fork): Likewise.
	* linux-nat.h (class linux_nat_target): Likewise.
	* remote.c (class remote_target) <follow_fork>: Likewise.
	(remote_target::follow_fork): Likewise.
	* target-delegates.c: Re-generate.
	* target.c (default_follow_fork): Likewise.
	(target_follow_fork): Likewise.
	* target.h (struct target_ops) <follow_fork>: Likewise.
	(target_follow_fork): Likewise.