Fix magic constants in backed enum values

Fix GH-8777

Author: iluuu1994

Zend/tests/enum/magic-constants.phpt

@@ -0,0 +1,14 @@
+--TEST--
+Backed enums can contain magic constants
+--FILE--
+<?php
+
+enum Foo: string {
+    case Bar = __FILE__;
+}
+
+echo Foo::Bar->value, "\n";
+
+?>
+--EXPECTF--
+%smagic-constants.php

Zend/zend_compile.c

@@ -10474,6 +10474,9 @@ static void zend_eval_const_expr(zend_ast **ast_ptr) /* {{{ */
 		case ZEND_AST_NAMED_ARG:
 			zend_eval_const_expr(&ast->child[1]);
 			return;
+		case ZEND_AST_CONST_ENUM_INIT:
+			zend_eval_const_expr(&ast->child[2]);
+			return;
 		default:
 			return;
 	}