Avoid new SSA var for ASSIGN_OBJ_REF without RC inference

Previously, this variable was necessary because of auto-vivification on
UNDEF/null/false. It's now only used for RC inference, as auto-vivification has
been removed.

This implicitly solves an inference problem for $obj->bar &= $obj; where we get
a new variable for both literal references to $obj, with the first one getting
the RCn flag, and the second one getting the MAY_BE_REFERENCE flag. Thus, the
first variable will be missing the reference type, causing a false-positive type
inference warning.

If we want to verify RC inference at some point we'll need a better solution.

Closes GH-13233

Author: iluuu1994

Zend/Optimizer/zend_inference.c

@@ -3157,7 +3157,7 @@ static zend_always_inline zend_result _zend_update_type_info(
 			}
 			break;
 		case ZEND_ASSIGN_OBJ_REF:
-			if (opline->op1_type == IS_CV) {
+			if (opline->op1_type == IS_CV && ssa_op->op1_def >= 0) {
 				tmp = t1;
 				if (tmp & MAY_BE_OBJECT) {
 					tmp |= MAY_BE_RC1 | MAY_BE_RCN;

Zend/Optimizer/zend_ssa.c

@@ -607,7 +607,7 @@ static zend_always_inline int _zend_ssa_rename_op(const zend_op_array *op_array,
 			}
 			break;
 		case ZEND_ASSIGN_OBJ_REF:
-			if (opline->op1_type == IS_CV) {
+			if ((build_flags & ZEND_SSA_RC_INFERENCE) && opline->op1_type == IS_CV) {
 				ssa_ops[k].op1_def = ssa_vars_count;
 				var[EX_VAR_TO_NUM(opline->op1.var)] = ssa_vars_count;
 				ssa_vars_count++;