IRA+LRA: Change return type of predicate functions from int to bool

gcc/ChangeLog:

	* ira.cc (equiv_init_varies_p): Change return type from int to bool
	and adjust function body accordingly.
	(equiv_init_movable_p): Ditto.
	(memref_used_between_p): Ditto.
	* lra-constraints.cc (valid_address_p): Ditto.