cfg+gcse: Change return type of predicate functions from int to bool

cfg+gcse: Change return type of predicate functions from int to bool

Also change some internal variables from int to bool.

gcc/ChangeLog:

	* cfghooks.cc (verify_flow_info): Change "err" variable to bool.
	* cfghooks.h (struct cfg_hooks): Change return type of
	verify_flow_info from integer to bool.
	* cfgrtl.cc (can_delete_note_p): Change return type from int to bool.
	(can_delete_label_p): Ditto.
	(rtl_verify_flow_info): Change return type from int to bool
	and adjust function body accordingly.  Change "err" variable to bool.
	(rtl_verify_flow_info_1): Ditto.
	(free_bb_for_insn): Change return type to void.
	(rtl_merge_blocks): Change "b_empty" variable to bool.
	(try_redirect_by_replacing_jump): Change "fallthru" variable to bool.
	(verify_hot_cold_block_grouping): Change return type from int to bool.
	Change "err" variable to bool.
	(rtl_verify_edges): Ditto.
	(rtl_verify_bb_insns): Ditto.
	(rtl_verify_bb_pointers): Ditto.
	(rtl_verify_bb_insn_chain): Ditto.
	(rtl_verify_fallthru): Ditto.
	(rtl_verify_bb_layout): Ditto.
	(purge_all_dead_edges): Change "purged" variable to bool.
	* cfgrtl.h (free_bb_for_insn): Change return type from int to void.
	* postreload-gcse.cc (expr_hasher::equal): Change "equiv_p" to bool.
	(load_killed_in_block_p): Change return type from int to bool
	and adjust function body accordingly.
	(oprs_unchanged_p): Return true/false.
	(rest_of_handle_gcse2): Change return type to void.
	* tree-cfg.cc (gimple_verify_flow_info): Change return type from
	int to bool.  Change "err" variable to bool.