Allocate map_ptr for mutable_data during preloading

We need to discard objects in the class constants if they happened
to be evaluated during preloading. To allow doing so, we need to
use mutable_data, which will place the evaluated constants into
a separate table.

Author: nikic

Zend/zend_compile.c

@@ -7687,6 +7687,7 @@ void zend_compile_class_decl(znode *result, zend_ast *ast, bool toplevel) /* {{{
 	if (CG(compiler_options) & ZEND_COMPILE_PRELOAD) {
 		ce->ce_flags |= ZEND_ACC_PRELOADED;
 		ZEND_MAP_PTR_NEW(ce->static_members_table);
+		ZEND_MAP_PTR_NEW(ce->mutable_data);
 	}
 
 	ce->ce_flags |= decl->flags;

ext/opcache/tests/preload_enum.inc

@@ -4,3 +4,4 @@ enum MyEnum {
     case Foo;
     case Bar;
 }
+var_dump(MyEnum::Bar);

ext/opcache/tests/preload_enum.phpt

@@ -14,7 +14,10 @@ if (PHP_OS_FAMILY == 'Windows') die('skip Preloading is not supported on Windows
 <?php
 
 var_dump(MyEnum::Foo);
+var_dump(MyEnum::Bar);
 
 ?>
 --EXPECT--
+enum(MyEnum::Bar)
 enum(MyEnum::Foo)
+enum(MyEnum::Bar)