cselib+expr+bitmap: Change return type of predicate functions from int to bool

gcc/ChangeLog:

	* cselib.h (rtx_equal_for_cselib_1):
	Change return type from int to bool.
	(references_value_p): Ditto.
	(rtx_equal_for_cselib_p): Ditto.
	* expr.h (can_store_by_pieces): Ditto.
	(try_casesi): Ditto.
	(try_tablejump): Ditto.
	(safe_from_p): Ditto.
	* sbitmap.h (bitmap_equal_p): Ditto.
	* cselib.cc (references_value_p): Change return type
	from int to void and adjust function body accordingly.
	(rtx_equal_for_cselib_1): Ditto.
	* expr.cc (is_aligning_offset): Ditto.
	(can_store_by_pieces): Ditto.
	(mostly_zeros_p): Ditto.
	(all_zeros_p): Ditto.
	(safe_from_p): Ditto.
	(is_aligning_offset): Ditto.
	(try_casesi): Ditto.
	(try_tablejump): Ditto.
	(store_constructor): Change "need_to_clear" and
	"const_bounds_p" variables to bool.
	* sbitmap.cc (bitmap_equal_p): 	Change return type from int to bool.