Bool-ify stap-probe.c and stap-related code on i386-tdep.c

Bool-ify stap-probe.c and stap-related code on i386-tdep.c

This simple patch converts a bunch of "int"s to "bool" on stap-probe.c
and on the stap-related code present on i386-tdep.c.

Pushed as obvious (+ I'm the maintainer of this code).

gdb/ChangeLog:
2019-05-16  Sergio Durigan Junior  <sergiodj@redhat.com>

	* i386-tdep.c (i386_stap_parse_special_token_triplet): Change
	return type to 'bool'.  Adjust comment.  Use 'bool' when
	appropriate.
	(i386_stap_parse_special_token_three_arg_disp): Likewise.
	* stap-probe.c (stap_parse_argument_1): Likewise.
	(stap_is_operator): Likewise.
	(stap_is_generic_prefix): Likewise.
	(stap_is_register_prefix): Likewise.
	(stap_is_register_indirection_prefix): Likewise.
	(stap_is_integer_prefix): Likewise.
	(stap_generic_check_suffix): Likewise.
	(stap_check_integer_suffix): Likewise.
	(stap_check_register_suffix): Likewise.
	(stap_check_register_indirection_suffix): Likewise.
	(stap_parse_register_operand): Likewise.
	(stap_parse_single_operand): Likewise.
	(stap_parse_argument_1): Likewise.
	(stap_probe::get_argument_count): Likewise.
	(stap_is_operator): Likewise.